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Title: The Library of Work and Play: Electricity and Its Everyday Uses

Author: John F. Woodhull

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*** START OF THE PROJECT GUTENBERG EBOOK THE LIBRARY
OF WORK AND PLAY: ELECTRICITY AND ITS EVERYDAY USES
***

THE LIBRARY OF WORK AND
PLAY
Electricity and Its Everyday Uses

THE LIBRARY OF WORK AND PLAY
Carpentry and Woodwork
By Edwin W. Foster

Electricity and Its Everyday Uses
By John F. Woodhull, Ph.D.

Gardening and Farming
By Ellen Eddy Shaw

Home Decoration
By Charles Franklin Warner, Sc.D.

Housekeeping
By Elizabeth Hale Gilman

Mechanics, Indoors and Out
By Fred T. Hodgson

Needlecraft
By Effie Archer Archer

Outdoor Sports, and Games
By Claude H. Miller, Ph.B.

Outdoor Work
By Mary Rogers Miller

Working in Metals
By Charles Conrad Sleffel.

Drawing by J. Hodson Redman
Harold Sending the C. Q. D. Message (See page 355)

The Library of Work and Play
ELECTRICITY AND ITS
EVERYDAY USES
BY JOHN F. WOODHULL, PH.D.
McGOWEN-MAIER & CO.
Chicago, Ill.

ALL RIGHTS RESERVED, INCLUDING THAT OF TRANSLATION
INTO FOREIGN LANGUAGES, INCLUDING THE SCANDINAVIAN
COPYRIGHT, 1911, BY DOUBLEDAY, PAGE & COMPANY

PREFACE
Why do we pursue one method when instructing an individual boy out of
school, and a very different method when teaching a class of boys in
school?
The school method of teaching the dynamo is to begin with the bar magnet
and, through a series of thirty or forty lessons on fundamental principles,
lead up to the dynamo, which is then presented, with considerable attention
to detail, as a composite application of principles. This might be styled the
synthetic method. He who teaches a boy out of school is pretty likely to
reverse this order and pursue the analytic method. The class in school has
very little influence in determining the order of procedure. The lone pupil
with his questions almost wholly determines the order of procedure. Out of
school no one has the courage to deny information to a hungry boy; in
school we profess to put a ban upon information giving, and we do quite
effectually deaden his sense of hunger. The school method rarely yields
fruit which lasts beyond the examination period; on the other hand, a
considerable number of boys have become electrical experts without the aid
of a school. This book is the story of how my boy and I studied electricity
together. We have had no other method than to attack our problems directly,
and principles have come in only when they were needed.
My boy had learned to read when very young by having stories read to him
while he watched the printed pages. The construction of sentences out of
words and words out of letters had come to him very incidentally but all in
due time, and when he first went to school rather late in life for a beginner
he found himself more proficient than the other boys of his own age both in
reading and in understanding the printed pages. I could see no good reason
why he should not pursue the same method in studying electricity.
We live in a modern apartment house in a great city. My boy likes to visit
engine rooms and talk with the engineers about their machinery. His mother
and I always encourage him to talk with us about the things in which he is
most interested. If the family is alone at dinner, he is quite likely to lead the
conversation into the field of electricity. When particularly burdened with

my work I have learned to find relief by giving an afternoon to Harold, who
generally takes me to some electrical store or power station or to ride by
electric train out into the country.

CONTENTS
CHAPTER PAGE
I. The Dynamo and The Power Station 3
II. Dynamo continued—The Magnet 11
III. The Ammeter 25
IV. The Wattmeter 35
V. The Electric Motor 43
VI. Applications of the Electro-magnet 57
VII. Electric Heating 97
VIII. Applications of Electric Heating 107
IX. Lighting a Summer Camp by Electricity 160
X. How Electricity Feels 168
XI. The Electric Sparking Equipment for a Gasolene Engine 178
XII. Electricity From Central Stations 204
XIII. Electricity From an Old Mill 218
XIV. Doing Chores by Electricity 240
XV. Electric currents from Chemical Action and Chemical 248
Action from Electric Currents
XVI. Electrocution at Millville 271
XVII. The Telephone 274
XVIII. Electric Bell Outfit for the Cottage 296
XIX. Using Electricity to Aid the Memory 300
XX. The Electric Brick Oven 305
XXI. Electric Waves 309
XXII. Ringing Bells and Lighting Lamps by Electric Waves 324
XXIII. Telegraphing by Electric Waves 329
XXIV. Halley's Comet and Electric Waves 333
XXV. How the Idea of a Universal Ether Developed 339
XXVI. Electric Currents Cannot Be Confined to Wires 349
XXVII. Wireless Telegraphy In Earnest 355

ILLUSTRATIONS
Harold Sending the C. Q. D. Message Frontispiece
FACING PAGE
Testing a Generator 8
Wiring 16
Wattmeter 40
Testing the Telegraphy Outfit 62
Electric Bell 72
Feeling Electricity 174
Operating the Switchboard 204
Induction Coil of a Wireless 330

ELECTRICITY AND ITS EVERYDAY USES

I

THE DYNAMO AND THE POWER STATION
ne day Harold expressed a desire to see the dynamos, five miles away,

O which furnish the electric light in our apartment. So I told him to invite
his best friend to accompany us and we would go.
When we were some distance from the station the boys noticed the very tall
chimneys and inquired why tall chimneys were needed for dynamos. I
explained that the dynamos were run by steam-engines, and steam-engines
required the burning of coal. "Oh!" said Ernest, Harold's friend, "I read in
the paper that electricity is the rival of steam and is going to drive out the
steam-engine." I suggested that we were about to see some steam-engines
driving electricity out of that power station. But more seriously, I explained
that steam-engines were used for many years as locomotives to draw the
trains on the elevated railroads of New York City, and when at last they
were displaced by electric trains some people thought that it was a case of
electricity driving out steam, whereas what had really happened was that
the steam power for running those trains had been concentrated at a central
station, and its power was merely transmitted to the trains by means of
electricity. The trains were, therefore, run by steam power quite as much as
ever. In like manner, the surface cars of New York a few years ago were run
by a cable, which was merely a very long belt used to transmit to the cars
the power of steam-engines located at a central station. When they were
changed to electric cars, electricity became the successful rival of nothing
else than a twisted wire cable. The cars still run by steam power as before,
but that power is transmitted by electricity instead of the discarded cable.
Steam has driven out the horse as a power for drawing street cars, and
electricity has enabled us to gather all the steam engines into central
stations, where now they are furnishing the power for moving surface,
elevated, and subway cars for street traffic, as also trains for suburban
travel. Central station steam-engines are producing a vast amount of power,
distributed all over the city by means of electricity, for doing a great variety

of work and for furnishing electric light and heat, all of which we shall
presently study. "Just before we go into this central station, can you tell me
how the elevator is run in our apartment house?" "It is an electric elevator,"
said Harold. "And where does the electricity come from?" I inquired. "Well,
I know that it comes from the street mains, but do they come from this
power station?" "Yes," said I, "and we will now go in and see the steam-
engines which lift you up stairs many times each day by sending electricity
to run that elevator. If you choose to do so, you may claim for purposes of
discussion that your elevator is run by steam."
As we entered the building we came first to the dynamo room and both
boys noticed that the tone which met their ears was that which I had
produced for them in the telephone the night before. "I shall try to show you
before we get through," I said, "that these dynamos are doing something
which makes iron pulsate sixty times a second and that that is the cause of
the pitch of this tone. But let us begin with the coal which is the source of
all this power.
"This particular station at the present time is burning forty tons of coal an
hour. That is as much as Mr. —— uses to heat his twelve-room house for a
whole year. One pound of coal is capable of liberating enough energy to
supply 5¾ horse-power for an hour. (Written for short 5¾ H.P.H.) One ton
of coal is capable of furnishing (2,000 × 5¾) 11,500 H.P.H. Forty tons
would yield 460,000 H.P.H. But the best furnaces, boilers, and steam-
engines are terribly wasteful of energy. About nine tenths of all this energy
is wasted and only one tenth, or about 46,000 horse-power per hour, is
delivered by the steam-engines to the dynamos.
"Coal is already scarce in the world and the supply is rapidly being
exhausted. Meanwhile we are growing more dependent upon coal. A
century ago we used scarcely any power except that of men, horses, and
oxen, and what little heat men then used came chiefly from wood. They
lived in cold houses, attended cold churches and schools, did not ride in
steam or electric cars, and did not have power plants. Our wood is nearly all
gone, our coal is going, and we are very rapidly growing more dependent
upon heat and power, our chief source of which is coal. Wind power is too
uncertain to depend upon, and we turned our backs upon water-power when
we began to crowd into cities. What little water-power there is, however, is
nearly all in use.

"There is great need both that we learn how to save the major part of the
energy of the coal which we now waste, and that we find a substitute for the
coal to use when that is gone.
"A part of the heat from the forty tons of coal which is being burned in this
particular power plant goes into the water in the boilers. It converts this
water into steam. The steam, if free to expand into the air, would occupy
about one thousand seven hundred times the volume of the water. We
compel it to expand through the cylinders of the steam-engine, using its
force of expansion to make wheels go around—to make the dynamo
revolve. These dynamos are not devices for producing power but merely for
transmitting the power of these steam-engines to far away places where it
may be used, as, for instance, in our apartment house, where we are
unwilling to walk upstairs and want some power to carry us.
"Our own apartment is fifty feet above the street. I weigh one hundred and
sixty-five pounds. If I walk up stairs from the street to our apartment in one
minute, which is the rate of a rather slow elevator, I work at the rate of one
quarter of a horse-power. One hundred and sixty-five pounds raised two
hundred feet in one minute requires one horse-power. You boys each weigh
about half as much as I do, and if one of you walks up the same stairs in one
minute you exert half the power that I do, or if you run up the stairs in half a
minute you exert the same power, that is, one quarter of a horse-power.
When we three walk up together in one minute we exert one half horse-
power. If we all three run up the stairs in half a minute we expend one
horse-power. Now, the speed of elevators for apartment houses is about one
hundred feet a minute. We are unwilling to walk up stairs, not because we
are lazy but because we have the New York haste, and so we employ
elevators which run at the rate of about one hundred feet a minute.

Photograph by Helen W. Cooke
Testing a Generator

"These dynamos enable us to employ the power of this central station to run
the elevator in our apartment house. Here is a dynamo rolling over now in
the act of sending out power, some of which goes to that elevator; and
standing beside it is another waiting to be used when necessary. Examining
these dynamos, we find that they are composed of nothing else than iron
and copper. About all that we can say of these mysterious machines is that
the moving iron generates the electricity and the copper leads it away.

"Each one of these dynamos has many
hundred tons of iron in it. A huge wheel of
iron, thirty-two feet in diameter, one
hundred feet in circumference, portions of
which are surrounded by insulated copper
conductors, forms the centre-piece of the
machine. This movable part weighs four
hundred tons. Around about this is a fixed
ring of iron, portions of which are
surrounded by insulated copper
conductors. Ordinarily the ring which is
stationary is called 'the field,' and the
wheel, which rotates, is called 'the Fig. 1
armature,' although these terms are
sometimes reversed for certain reasons. The movable part in these machines
rotates about once a second, that is, its circumference moves a little faster
than a mile a minute. The iron moving at this high rate of speed creates
ether streams or electric currents, which are led off by the copper
conductors. The generation of electricity on a large scale requires large
masses of iron and high velocity."
I noticed that the boys stood before this machine in a state of utter
bewilderment, bewildered as a man who is told that what he had considered
north is really south, bewildered as a man who, having wandered through a
maze of city streets, looks up at length and unexpectedly finds the building
he has been seeking towering before him. The questions they asked were
entirely without thought. "What is inside of it?" "Simply more iron and
copper, such as you see on the surface," I replied. "But what makes it go?"
"The steam engines, of course, four of which you see, are coupled directly
to each dynamo." "But where does it get its electricity?" "Don't forget that
you are looking at a generator of electricity. Big mass of iron—rapid
motion! That is the whole truth. But it cannot satisfy you as an answer until
you have become used to it. We have seen all that we ought to see here to-
day. Let us drop the whole matter now, but return to my laboratory to-
morrow, and I will give you the next step which will help you."
The boys did no talking upon their return journey. Whether one may say
they were thinking or not I cannot tell, but certainly their ideas were

incubating.

II

THE DYNAMO, CONTINUED—THE MAGNET
hen we had gathered at my laboratory the next day I took down a

W spool of one pound No. 24 cotton-covered copper wire (Fig. 2 A),
which had its centre filled with wire nails. The boys had seen it
before and remembered it. With flexible wires I connected the two ends of
the wire on this spool to a sensitive ammeter, B, which had its zero in the
middle of the scale, and I laid down upon the table a bar magnet, C.

Fig. 2

"Here," I said, "is a dynamo complete." The bar magnet furnishes the 'field'
and this spool of copper wire, A, which I will move back and forth
immediately over the magnet from end to end, is 'the armature.' D and e are
the line wires and the circuit is completed through the ammeter to show
whether we are generating electricity. And now as I move this armature
along the field you see the needle of the ammeter move to the right from
zero to ten. When the armature is moved in the opposite direction along the
field the needle moves in the opposite direction past zero and on to ten at
the left. The moving of the needle in the ammeter shows that we are

generating electricity. The swinging to and fro of the needle shows that we
are generating an alternating current of electricity. It is a mere matter of
detail whether we move the armature or the field, as I will show you by
letting the spool A rest quietly upon the table and moving the magnet to and
fro lengthwise across the end of the spool. Or I may accomplish the same
results by moving them both in opposite directions. It is simply necessary
that they move with reference to each other. Some dynamos are made with
stationary fields and rotating armatures, some with stationary armature and
rotating fields, and some with both parts designed to rotate in opposite
directions.
"Magnetism is not confined to the magnet. It extends more or less widely
into the region about it. It is this region affected by the magnet that we
designate its magnetic field. By bringing this sensitive compass needle into
the region of this bar magnet from all directions, I show you that it has a
slight power to change the direction of the needle when about a foot away.
This power grows rapidly greater as the distance grows less. Of course its
field extends rather indefinitely, but we may say that this particular magnet
has an appreciable field extending about one foot in all directions from it.
We find upon examination that some magnets have bigger and stronger
fields than others, that all have their strongest fields when first magnetized
and lose their strength gradually, but never entirely. We find that hardened
iron and steel hold magnetism longer than soft iron, but all iron is
magnetized somewhat at all times. Iron that is feebly magnetized can be
made into a strong magnet by bringing it into a strong magnetic field. The
earth is a feeble magnet, and that is why it gives direction to the compass
needle. That is also probably the reason why every piece of iron upon the
earth is a magnet, or, to put the cause back another step, we may say that
whatever causes the earth to be a magnet also causes every piece of iron
upon the earth to be likewise a magnet.
"But thanks to Oersted in Denmark in 1819 and Faraday in England in 1821
and Joseph Henry in Albany, N. Y., in 1827, we have learned to make
exceedingly powerful magnets by sending a current of electricity in a whirl
around the iron. This is the meaning of the coils of copper wire around iron
cores in the dynamo, in electric bells, in telegraph sounders, in motors, etc.,
etc. To prevent the electric current from taking the shortest route, through
the iron core or through the successive layers of copper wire, the iron core

and the wire must be covered with something like wood or paper or cotton
or silk or rubber—such things as electricity does not readily pass through—
that is, insulating material.
"Joseph Henry, while teaching in the Albany Academy, was the first to
make electro-magnets. There was no such thing as wire covered with an
insulating material then in the market, and he wound all his wire with silk
ribbon. But in the year 1834 he made magnets which lifted thirty-five
hundred pounds, to the astonishment of every one. A pair of such electro-
magnets as I have here (Fig. 3), each consisting of one pound of No. 24
cotton covered copper wire, eight hundred feet long, wound in one thousand
turns about an iron core two inches in diameter, will lift several hundred
pounds: much more than we three can lift, as I shall now show you."

Fig. 3

The cores of the two magnets were bolted fast to an iron beam, and a large
bar of iron with a ring in it was laid across the other free ends of the magnet
cores. I made connections with the electric lighting circuit (that in my
laboratory is what is called a direct current), and sent a current of electricity
around the coils. The two boys and I tugged at the ring in the iron bar to no
avail. We were unable to pull the iron bar away from the magnet. But when
I opened the switch and cut off the electric current, one boy with one finger
in the ring lifted the bar with perfect ease.
"Electro-magnets are now made with a magnetic intensity 90,700 times that
of the earth's magnetism. Electro-magnets are used for hoisting iron

castings weighing many tons. Here is a picture of an electro-magnet lifting
a whole wagon load of kegs of nails from the wagon to the hold of a ship.
"Electro-magnets are our only means of utilizing electricity for power. It is
the pull of electro-magnets that moves the electric car. Electro-magnets are
now used for pulling all the trains out of the Grand Central Depot in New
York City.
"Let us now compare the strength of our electro-magnet with that of the bar
magnet used in our former experiment."
I opened and closed the switch, which sent the electric current through my
magnet coils at frequent intervals, and the two boys, each with a compass
needle, searched the field for magnetic effects. They found that the
magnetic field extended six or eight feet, but this piece of research was
broken up by a new idea which appeared to strike them both at the same
instant, for they shouted both together, "Let's use this electro-magnet in
place of the bar magnet for our dynamo experiment!"

Photograph by Helen W. Cooke
Wiring

"That is surely the next step in our programme," said I, "but you will need a
steam-engine to move an armature in this magnetic field, will you not,
judging from the struggle we had with that iron bar a few minutes ago?"
The boys looked quite hopeless until I said, "The best thing about the
electro-magnet remains yet to be told. You have perfect control of its
strength by changing the amount of electricity which you send around the
coil.

"By means of an instrument which works like the motorman's controller on
the electric car, I may control the amount of electricity which flows, just as
well as you may control the flow of water by a faucet or stop-cock. By this
means I will control the strength of the magnet so that you may move the
armature in your dynamo experiment.
"In 1821, Faraday, at the Royal Institution, London, learned that he could
produce magnetism by means of the electric current, and, in 1831, he
learned that the reverse was also true, namely, that he could produce
electricity from magnetism. This idea coming as the result of ten years of
incessant search made him shout and dance like a child. You are feeling a
little of the pleasure of his discovery."

Fig. 4

I then fastened one of the coils upon the table underneath a small bench
(Fig. 4) and sent an electric current around it. The other coil, B, connected
with the ammeter was pushed back and forth along the surface of the bench
over this coil. The boys found that the more electric current I sent around
the coil A, that is, the stronger I made the magnetic field, the harder it was
to move the coil B. They found that the nearer B was to A the harder it was
to move it. They found that the faster they moved B the more electricity was

produced. They tried laying B upon its side upon the bench and thus moving
it. They tried taking B off the bench and moving it on all sides of A. They
found it much harder to move in some ways than in others, but in all cases
they found that the harder they had to work the more electricity was
developed, as was shown by the ammeter.
"The dynamo is any machine which will convert mechanical work into
electricity. The magneto is one form of a dynamo which you have used
much at the summer cottage, but have never seen the inside of. Here are
several (see Figs. 5, 6, and 8) which I will let you examine inside and out,
and with these I must leave you to yourselves for a time."
When I returned I asked the boys why these dynamos were called
magnetos. "Because they have steel magnets for their fields," they replied.
"There are several magnets bent in the shape of a horseshoe."
"Yes," I said, "in this case the field is made stronger by taking several
magnets. Have you noticed any armature?" "Yes, it is made of iron with
insulated copper wire wound around it."
"Please recall that the amount of energy you expend in going upstairs
depends on two things: (1) your weight and (2) the speed with which you
move. Also recall that the amount of electricity you could generate with a
dynamo depended upon the amount of energy you expended. Therefore, the
strength of the electric current which this machine may produce depends
upon two things: (1) the strength of the magnetic field against which you
must pull and (2) the speed of the motion of the armature. Evidently this
field is made as strong as it is possible to make it with steel magnets. Now
is there any device for giving high speed to the armature?"
"Yes, indeed," said the boys, "one has a pulley so that it may be connected
by a belt with a gas engine, and the others have each a large cog-wheel
working into a smaller one. We found in one of them that a single
revolution of the crank gave six revolutions to the armature."
I found that the boys had made large-sized drawings of the parts, and were
preparing to report on the magneto as a form of dynamo at the next meeting
of the Science Club, which we had started among the boys in school.
"I will loan you some apparatus so that you may give a very interesting
demonstration on that subject," said I, "only let me show you how to use it

first. Connect the binding posts D and E of
this magneto (Fig. 5) with my ammeter.
Turn the crank very slowly and notice that
the needle of the ammeter swings to and
fro with each revolution of the armature.
That shows that you have not only a
dynamo, but an alternating current
dynamo.
"Now
Fig. 5 connect
the
binding posts d and e of this magneto (Fig.
6) with a short piece of copper wire. Turn
the crank and you notice that this dynamo
rings two electric bells. Turn slowly and
you notice that the alternations of the
current are numbered by the strokes on the
bells. The hammer swings to and fro just
as the needle of the ammeter did. Each bell
therefore receives one stroke of the
hammer for each revolution of the
armature. Now try to turn the crank Fig. 6
steadily at the rate of one revolution per
second. The armature is making six revolutions, or cycles, per second and
you now have not only an alternating current dynamo but a six-cycle
alternating current dynamo. The lighting circuit used in our apartment is a
sixty-cycle alternating current. To be sure the armature of the dynamo which
generates that current revolves only once a second, but it carries coils
enough upon its rim to make that number of alternations.
"Now connect this telephone receiver with the binding posts D and E of this
magneto (Fig. 7). Unscrew the cap of the receiver. Move to one side the
iron diaphragm and turn slowly the crank of the magneto. Notice that the
diaphragm vibrates in time with the alternations of the dynamo. Replace the
diaphragm, screw on the cap, hold the receiver to your ear and turn the
crank as fast as you can. You will probably be able to make about sixteen

cycles per second. The receiver in that case
is giving forth a sound of the same pitch as
a sixteen-foot closed organ-pipe.
"Connect
the
telephone
receiver
to the
binding
posts D
Fig. 7 and E of
this
magneto (Fig. 8), and by means of a belt
connect the pulley to this series of cog- Fig. 8
wheels. Now you may turn the crank and
readily make the armature revolve at the
rate of sixty cycles per second, and you notice that you get the same tone
that we heard in the dynamo room of the power station and the same tone
the telephone receiver gave when I connected it to a coil in our apartment.
The tone which is produced by sixty vibrations per second is very nearly
that of the C two octaves below middle C on the piano. Try it along with the
piano and you will find it a little flat. This string on the piano is making
sixty-four vibrations per second.
"Now connect this miniature telephone
switchboard lamp with the magneto (Fig.
9) and turn the crank fast. The lamp lights
up to full brilliancy and you notice that the
light is steady, although it is made by an
alternating current passing through the
filament in one direction, stopping entirely,
and then passing in the opposite direction.
The filament has no time to cool off,
provided you turn fast enough, but try
Fig. 9 turning a little slower and you will notice
the flickering of the lamp."

III

THE AMMETER

Fig. 10

t the last meeting of the Science Club so many questions were asked,

A which the demonstrators could not answer, that a programme
committee, to whom such questions might be referred thereafter, was
appointed. It was made the duty of this committee to assign to various
members the task of searching for satisfactory answers, and when the
material was ready to be reported to the club, the programme committee
determined the time and order of presentation. I found that I had been made
an honorary member of this committee and that it was expected that I
should steer the committee. I told them that I accepted this appointment

with the understanding that the fellow who steers is always the smallest
man in the crew, and if they would do all the work I would enjoy the
honorary title of cockswain. Secretly, however, I appreciated that this was
in effect adding several courses to my already rather heavy programme. I
must, under the régime, direct a large number of inexperienced students in
library research, in laboratory research, and in the art of giving
demonstrations with apparatus and experiments to audiences.
The most urgent questions, as also those which were next in the natural
order, concerned the ammeter. I told the committee to make that the subject
of the next meeting and to send to my laboratory on a certain day the person
or persons whom they might appoint to report upon it.
I find that the boys never come singly, but
generally in pairs. When the boys came they
found lying upon the table an ammeter (Fig. 11).
I told one of them to take out the three screws in
the front and remove the face of the instrument.
I had told the boys that the instrument cost sixty
dollars and that letting them open it was like
letting them open my watch. As soon as the face
came off one of the boys exclaimed that from
my reference to the watch he had expected to
see very complicated machinery with many
Fig. 11 wheels, but from the exceeding simplicity of the
mechanism he could not see why it should cost
sixty dollars. I told him that although it was a fine piece of workmanship it
was fortunately very easy to understand, and I asked them if it reminded
them of anything else that they had ever seen. After a few moments of
reflection they agreed that it was very much like one of the magnetos.
"Well," said I, "where is the field?"
"Is this horseshoe arrangement a magnet?" they inquired.
"There is a compass needle right at your hand waiting to answer that
question," I replied. They immediately found that it was a magnet. "Well," I
said, "to be really sure that it is a magnet you must find a portion of it that
will repel a portion of your compass needle as well as other portions in both
horseshoe and needles which attract each other." Whereupon, they found

that the portion marked N (Fig. 13) repelled the
blue end of the compass needle and attracted
strongly the bright end of the needle, while the
portion marked S did the reverse. "We will call
N and S the poles of the magnet. This is simply
a steel bar magnet bent into the shape of a
horseshoe."
"You told us,"
remarked one of the
boys, "that steel
magnets gradually
lose their strength.
How then can this be
correct as a
measuring
instrument?" Fig. 12
"It is the purpose of
the iron case to enable this magnet to retain its
magnetism, and if you will examine its field, as
we did that of another magnet upon a former
occasion, you will find that although this is a
Fig. 13 strong steel magnet its field does not extend
outside of the iron case. It is as though we could
box up magnetism and keep it from escaping.
"Now if this is like the magneto, where is the armature? The spool-like
thing between the poles of the magnet looks just like the armature in one of
the magnetos.
"Yes, it has an iron core with a coil of insulated wire around it, and you
remember that when an electric current is sent around a piece of iron, that
iron is made into a magnet, and if it is a magnet it must have poles. It is
very delicately poised upon a pivot and will act exactly like your compass
needle, which is also a little magnet with poles. I will send an electric
current through the wire which surrounds this armature, and you notice that
the needle which it carries moves to the right. Notice that the lower end of
this armature acts like the blue end of your compass needle in that it is

repelled from the pole N of the field and is attracted toward S of the field. In
like manner, the upper end or pole of the armature is repelled from S and
attracted to N of the field. The blue end of the compass needle is called its
north pole because it points north under the magnetic influence of the earth,
and so we may call the lower end of the armature its north pole.
"The electric current which I am sending through the armature comes first
through one ordinary 16-candle-power electric lamp which you see lighted
on this 'resistance board,' as it is called, and you notice that the needle
points to .5. This means that half an ampere of electricity is passing through
this lamp. I will now send the current through a 32-candle-power lamp, and
you notice that the needle points to one, indicating that one ampere is
required to light that lamp. But what prevents the needle from going farther,
and what brings it back to zero each time?" The boys discovered a very
small spring, like the hair spring of a watch, coiled around the pivot of the
armature. "So, then, one ampere of electricity gives magnetism to this
armature so that it may pull against its coiled spring hard enough to carry
the needle to the point one. Twice as much electricity will give it magnetism
enough to carry it to two, and so on across the scale.
"The full name of this instrument is Ampere meter, which by usage has
been shortened to ammeter. It was named in honour of André Marie
Ampère, who was born at Lyons, in France, in 1775, the year our
Revolutionary War broke out. He died in 1836. When Oersted made his
famous discovery of the action of an electric current upon a magnetic
needle, in 1819, Ampère was in middle life (forty-four), and took up the
same line of research with great vigour. The next year, 1820, he discovered
what you will doubtless enjoy rediscovering now.
"You will notice that the binding posts on the bottom of this ammeter are
marked, one positive, +, and the other, negative -. The electric current now
enters the instrument by the post marked + and after passing around the
armature leaves by the post marked -. I will reverse the connections and
thus send the current around the armature in the other direction, and you
notice that its poles are now reversed. The lower end which was formerly
the north pole of the armature has now become the south pole, as proven by
the fact that it is repelled from the south pole of the field and attracted to its
north pole. This carried the needle to the left, and inasmuch as the zero is in
the middle of the scale we may with this instrument both measure the

amount of current and tell its direction. You will recall that when we
connected the magneto with this instrument, it indicated that the magneto
sent the current first in one direction and then in the other, which we call an
'alternating current.' But you notice that the current which I am using in this
laboratory flows continuously in one direction. This is called the 'direct
current.' We shall find out how a dynamo may produce a direct current at
another time. Let us not forget, however, that we have repeated Ampère's
discovery, and found out that the direction in which we send the current
around an electro-magnet determines which end shall be its north and which
its south pole. If you will note carefully which way the wire is wound
around the armature you will see that when I send the current in at the
positive post it is passing around the north pole of the armature opposite to
the direction in which the hands of a clock move. If I reverse the current it
passes around the lower end of the armature in the same direction as the
hands of a clock move and then this end becomes a south pole. This is
'Ampère's rule,' and it is what candidates for admission to college are very
careful to learn.
"Before we replace the face of this ammeter I must call your attention to a
wire running by a short cut from one binding post to the other, s (Fig. 14).
Suppose a represents the wire around the armature. Electricity, like water,
goes more readily through a big conductor than a small one and more
readily through a short than a long conductor. If s and a were water pipes,
each having a stop-cock, we might easily adjust the cocks so that one tenth
of the water would go through a and nine tenths through s. Or, indeed,
without stop-cocks, the size and length of s and a might be so apportioned
that one tenth of the water would flow through a and nine tenths through s.
This is precisely the adjustment which has been made with reference to the
flow of electricity through this instrument. s is called a 'shunt.' When the
shunt is out all the current goes through a and when the shunt is in only one
tenth of the current goes through a. I have two other shunts, each of which
may be put in the place of s. With the second only one hundredth of the
current goes through a and with the third only one thousandth of the current
goes through a. Thus I have an instrument which will measure anything
from one thousandth of an ampere up to ten amperes.
"In this laboratory we pay about one cent for an ampere of electricity for
one hour. Twice as much coal must be consumed to furnish two amperes as

one, and twice as much coal must be consumed to
furnish an ampere for two hours as for one hour.
Hence we need an instrument which will keep account
of time as well as amount of current. Such an
instrument we must look into next.
"Just before we pass to that, however, let me ask if you
have ever heard of a 'shunt-wound' dynamo. Can you
guess from the way we have just used the word 'shunt'
what the expression could mean with reference to a
dynamo?" Without hesitation the boys told me that it
meant that the field and armature were wound parallel
to one another, as shown by diagram in Fig. 15. In Fig. 14
which case the electric current which the machine
generates divides, part of it going around the field and part around the
armature. Another type, called series-wound dynamos, is indicated by
diagram in Fig. 16, in which case the electric current goes through field and
armature in succession. Under either of these circumstances, how can the
armature move with reference to the field? The answer will appear in the
next chapter.

Fig. 15

Fig. 16

IV

THE WATTMETER
e were able to maintain connections between the binding posts of the

W ammeter and the movable armature of flexible wires because the
armature never moves more than one third of a revolution, but we
now wish to examine an instrument in which the armature must not only
make a complete revolution but must continue to revolve in the same
direction indefinitely. How are connections made so that an electric current
may pass from the fixed binding posts to the wire of the moving coil? I will
lift the cover off this instrument, which is called a wattmeter, and let you
find the answer to that question.
I sent through the instrument the current from a 32-candle-power lamp.
According to the ammeter, which was also in circuit, the amount was one
ampere.
The armature of the wattmeter revolved slowly and it was not long before
the boys reported that connections for the current were made by strips of
metal sliding on metal plates. The ends of the armature wire were fastened
one to one plate and the other to the other plate, and the metal strips brush
along over the surfaces of the plates. (That is why they are called "brushes,"
I said.) And the brushes slide from one plate to the other each time the
armature makes half a revolution. (That is, the brushes change the
connection and thus change the poles of the armature at the proper instant
so that they are always attracted to the poles of the field toward which they
are moving.) This is called a commutator.
Notice that while the ammeter was like the magneto in having a steel
magnet for its field, the wattmeter is like the dynamo in having electro-
magnets for both armature and field. Notice in the second place that this
instrument is an electric motor since it is made to revolve by an electric
current. If it were made to revolve by some other power it would generate
electricity and would then be called a dynamo. Indeed, let me tell you

something which must at present be nothing more than a puzzle to you.
Every machine, while it is being driven by an electric current as an electric
motor, is, at the same time, acting as a dynamo to generate a current in the
opposite direction. Notice in the third place that this is a shunt-wound
instrument. The current which is sent into the instrument divides, and part
of it goes through the field, while part goes through the armature. Motors,
as well as dynamos, are either shunt-wound or series-wound. But notice
finally that the axle on which the armature is carried has a cyclometer
arrangement which keeps account of the number of revolutions. The
armature is going slowly enough for us to count the revolutions. With watch
in hand we found that it made one hundred and twenty revolutions per
minute. I next brought the current to the wattmeter through a 16-candle-
power lamp and the ammeter, connected in series, showed that half an
ampere was passing. We counted the revolutions of the wattmeter and found
them to be sixty per minute.
Here, then, is a simple electric motor which will register the amount of
electricity we use. It will register the same amount whether we use one
ampere for one hour or half an ampere for two hours or two amperes for
half an hour. In any case this product is called one ampere hour. But the
words printed upon the dials of this instrument are not ampere hours, but
watt hours and the name of the instrument is wattmeter. This next requires
explanation. Follow me in a little roundabout journey and the matter will be
readily understood when viewed from another approach.

Fig. 17

When we were estimating the energy required to climb the stairs of an
apartment house, we needed to take into account two factors, (1) our weight
and (2) the time which we took in climbing them. The amount of coal
burned, steam generated, electricity produced, to run our elevator depends
upon two factors, (1) its weight and (2) its speed. That idea is fundamental.
Let us get at it in still another way. Suppose we have a mill pond, (Fig. 17,
A). We construct a penstock p and install a water-wheel, S, to operate a mill.
Our business increases and we install more machinery in our mill and must
have more power to run it. We have two ways of getting it, (1) we may
lengthen our wheel and enlarge our penstock so that a greater weight of
water will fall upon the wheel, or (2) we may lengthen our penstock and
move the wheel farther down so that the water will fall upon the wheel with
greater velocity. It is just so with the electric current. Like water it is driven
on in its course by pressure. The unit for electric pressure is called a volt. If
we wish to drive the wattmeter or any other electric motor twice as fast as
now, we may choose whether we shall do so by doubling the volts of
pressure or by doubling the amperes of quantity.

The electric pressure on our mains is about one-hundred and ten volts. We
three together weigh 330 pounds. Our elevator brought us up stairs at the
speed of 100 feet per minute. It requires one horse-power to raise 330
pounds 100 feet in a minute. The ammeter in the engine room showed that 7
amperes of electricity were sent through the motor of the elevator to bring
us up. That is, seven amperes at 110-volt pressure give one horse-power. In
the office building across the street where they use a 220-volt current 3½
amperes are required to take us up stairs at the same speed. It is necessary
that the same amount of coal be consumed to furnish the horse-power of
energy whether we supply it by means of seven amperes at 110 volts or 3½
amperes at 220 volts. You notice that the product is 770 in each case. The
name given to this product is watts. More accurately 746 watts of electrical
power are equivalent to one horse-power. The name of this unit
commemorates the famous inventor of the steam engine, James Watt (1736–
1819). His monument now overlooks the Clyde at his native town,
Greenock, Scotland.
To light a certain lamp, to heat a certain laundry iron, to furnish a certain
amount of power for an electric motor, we must have a definite number of
watts. We may choose whether we will have it at high or low voltage with
correspondingly low or high number of amperes.

Fig. 18

We will now connect with our laboratory current a 32-candle-power lamp,
an ammeter, and a wattmeter, all in series, Fig. 18, and in parallel with these
a volt meter. This last instrument indicates the electric pressure. Its
mechanism will be examined later. The volt meter indicates 110 volts and
the ammeter shows that one ampere is passing. The filament in the lamp

resists the passage of the current. It gets quite hot and gives forth as much
light as thirty-two candles. Its resistance is just such that 110 volts of
pressure send one ampere through it. We will now take the reading of the
wattmeter, note the time and read it again later. One hour later its index
showed that 110 watt hours of electrical energy had been converted into
light and heat. This at the usual rate, costs 1.1 cents, one cent per hundred
watt hours or ten cents per thousand watt hours, called a kilowatt hour. The
more common 16-candle-power lamp costs about half a cent an hour to
operate. It requires one horse-power to keep fourteen of them burning.

Photograph by Helen W. Cooke
Wattmeter

I will now take you to see the wattmeter which measures all the electric
energy used in this building. You note down its reading and the date and the
next time you come we will read it again and thus find out how much
electricity has been used for electric lights, for electric ventilating fans, for
electric elevators, for electric ovens, and electric irons in the school of
household arts, for electric motors to run lathes and other machines in the
school of technical arts, for electric experiments in my laboratories and
lecture room, for electric vacuum cleaners and, lastly, for pumping the pipe
organ in chapel.
I saw by the boys' faces as they departed what would be the next question
that they would bring to me. Knowing, however, that the hour was up, they
were too polite to press it then.

V

THE ELECTRIC MOTOR
n a few days I received a telephone message, asking if I could appoint an

I hour to meet the programme committee in my laboratory. I must confess
that my pleasure in these meetings had increased so much that I was
quite ready to slight other duties, if need be, to engage in them. Moreover,
since my business was education it was not difficult for me to regard these
meetings in the light of a duty quite as important as my regular class
instruction—perhaps more effective. At any rate the boys and I managed to
get together. May God forgive the man who essays to teach boys, but does
not love to be with them.
Of course at the last meeting of the Science Club every one wanted to know
how we ran a pipe organ by electricity. Moreover the Electrical Show was
coming on in the city, and cows were to be milked by electricity, dishes
were to be washed by electricity, rugs and furniture were to be cleaned by
electricity, and innumerable distracting and distressing things were to take
place. I told the boys that really only two kinds of things were to be done by
electricity at the show, and if they would give me two one-hour
appointments I would furnish them with the key to the whole show. We
might as well begin to-day with the pipe organ question.
A pipe organ is operated by air. It has bellows which are simply one form of
an air pump. A boy is often employed to turn a crank which works the
bellows. Down in the basement underneath our pipe organ I will show you
how a half-horse-power electric motor takes the place of a boy. We found a
dark and dirty corner where a boy used to stand and turn a crank every time
æsthetically inclined people enjoyed an organ recital in the room above.
Science, which has not been given credit for being humanitarian, put an
electric motor into that dark corner and sent the boy up stairs to hear the
music. The motor grumbled at the dirt in the corner and compelled the
janitor to keep it clean.

The electric motor, better than any device I know, enforces justice, but
never requires mercy, or at least rarely receives it. It comes nearer than any
other machine to paying back all that you put into it. It is most economical
when working up to its full capacity. I recommend that you look it over
carefully and after a few minutes tell me what you have seen in it.
The boys said that it looked just like a
dynamo. We must not forget that it is a
dynamo, but is here used as a motor by
sending an electric current through it. This
fact, that a dynamo might be driven by an
electric current and serve as a mover of
other machinery, was first publicly
exhibited in 1873 at the Vienna Exhibition,
and by many believed to have been
discovered by accident at that exhibit. But
why does it look like a dynamo? It has a Fig. 19
field whose magnetism is produced by an
electric current sent through coils of wire, and it has an armature whose
magnetism is likewise produced by the electric current. If it were used as a
dynamo, where would it get the electric current to magnetize its field? From
its own moving armature. Is it adapted for direct current? Yes. It has a
commutator and brushes. Is it shunt- or series-wound? Shunt-wound, as
shown by diagram in Fig. 20.
Suppose we treat the machine as a dynamo. Bring the ends of the line wire
together, thus, as we say, closing the circuit. By some external force let us
cause the armature to rotate and under the influence of the magnetic field it
will generate an electric current, part of which will pass through the field
and part through the line circuit. We may adjust the relative amount of wire
in field and line so that any portion of the current we choose will pass
through the field. The amount of current it will generate depends, (1) upon
the strength of the field and (2) upon the speed of the armature. Its field,
although never entirely without magnetism, is very feeble at first, and hence
in the first instance a very small current will be generated in the moving
armature. This, however, will strengthen the field slightly, and as the field is
strengthened the armature will generate more current, and thus by a mutual
reaction the machine gradually "builds up" to full strength.

When
now we
use the
machine
as a
motor, an
electric
current
must be
sent along
the line
wires in
the
opposite
direction
(Fig. 21)
from Fig. 21
Fig. 20 which it
would come out of the machine when
acting as a dynamo. It will then be noticed that, although the direction of
the current through the field is the same, whether the machine is used as a
dynamo or a motor, the direction through the armature, when used as a
motor, is the reverse of that when used as a dynamo.
You may perhaps be able to notice that the amount of wire on the field is
considerably more than that on the armature. Now if you will trace the
wires carefully you will find that there is provided a way of supplementing
the wire of the armature with some more wire in what is called the rheostat,
Fig. 22. This wire, or portions of it, is introduced into the armature circuit
when the machine first starts. When, however, the machine has started and
the armature is moving within the influence of a magnetic field, it plays the
part of a dynamo at the same time that it is acting as a motor. Two
conflicting and opposite electro-motive forces therefore exist in the
armature at the same time. In Fig. 22 the arrow a represents the direction of
the electro-motive force which is impressed upon the armature, and the
arrow b represents the counter-electro-motive force which the moving
armature develops.

This counter-electro-motive force, which
develops while the machine is in motion,
makes it unnecessary to hold back the
current longer by the extra resistance of
the rheostat and hence that is usually cut
out. Being used only for starting purposes
and looking like a box, it is generally
called the "starting box." If now it was
intended that this motor should run at a
constant speed, as is often the case, no
other governor would be needed than this
counter-electro-motive force, for whenever
the machine begins to go faster, on account
Fig. 22 of reduced load, its counter-electro-motive
force increases as the speed and holds in
check the impressed electro-motive force. This acts very perfectly as a
governor, and motors operate with notoriously constant speed under
variable loads. But, of course, in this present instance the motor is required
to work at a variable speed. It must pump air slowly for the soft passages of
music, and it must work the pump to its utmost for the very strong passages.

Fig. 23

To understand how an electric motor may pump an organ and have its speed
automatically controlled, let us examine the diagram in Fig. 23. The motor
m causes the shaft S to revolve, carrying the crank C around with it. The rod
r causes a b, the lower side of the bellows, to rise and fall, this side being
hinged at b. The side b c, is fixed. When the side a b is pushed upward by
the crank rod the valve f closes and the air in the compartment h pushes
open the valve g and enters the compartment j. The upper side d e, of this
compartment rises as it is filled with air. Weights K, K, K, rest on the top of
this and air ducts lead from this compartment to the pipes of the organ. The
keys of the organ operate air cocks which open and close the air ducts

connected with the organ-pipes. A chain connected with e passes around the
axle of the wheel l and has a weight W upon its lower end. The wheel l
carries a strip of brass n, which slides over metal points p, p, p, etc. The
successive points are connected by coils of wire to furnish resistance. This
series of coils is called a rheostat. The wires t and u form a loop from the
armature of the motor and connect this rheostat in series with the armature.
u is connected with the brass strip n. Notice that when the compartment j is
full of air and the side d e, is lifted to its greatest height the strip n is moved
to the lowest point p, and the electric current must pass from u through all
the resistance of the rheostat in order to get back to the armature by the wire
t. This makes the motor go very slowly. When d e sinks down, the strip n
moves to the upper points p, and the resistance is reduced step by step,
enabling the motor to quicken its speed and pump faster as more air is
required.
Small motors in order to be effective must travel at high speed. This motor
when moving at its highest speed makes 1,800 revolutions per minute. The
bellows on the other hand needs to be large and move slowly in order to be
efficient. Hence the motor is not in reality connected directly to the shaft S,
but causes the shaft to revolve by means of a series of pulleys and belts. The
pulley on the motor is three inches in diameter. It is connected by a flat
leather belt with a wheel thirty inches in diameter. When the motor
therefore, makes 1,800 revolutions per minute this wheel makes 180
revolutions per minute. The axle of this wheel carries a small cog-wheel
three inches in diameter and it is connected by a chain belt with a cog wheel
on the shaft S (Fig. 23). Thus this shaft revolves thirty times per minute,
that is, the rod r rises and falls each second. A pull of one pound on the rim
of the motor pulley will cause a pull of sixty pounds on the cogs of the
wheel upon the shaft S. If the second belt were leather, a sixty-pound pull
would cause it to slip on the smaller pulley. Hence the second belt is a steel
chain and the wheels have cogs, or sprockets, like a bicycle.
The organist before beginning to play closes a double-pole, single-throw
switch (Fig. 24), which sends the electric current to the motor.
The motor pumps air until the bellows is full, and if the organist delays
playing, the strip of brass n (Fig. 23) is carried below the lowest point p,
thus cutting off the current and stopping the motor. As soon as he uses some

of the air in the bellows, however, n rises
and makes contact with the points p and
the motor starts.
This suggests that a somewhat similar
thing is accomplished under electric cars
which have air brakes. An electric motor
pumps the air and compresses it in a tank.
When the pressure reaches a certain point,
say sixty pounds per square inch, it
automatically shuts off the electric current
Fig. 24 from the motor which works the pump.
But when the motorman uses some of the
air to apply the brakes to the wheels, and the pressure in the tank falls
below sixty pounds, the electric current is again automatically turned on to
the motor.
Of course if an electric motor can operate a pump to compress air it may
also work a pump to exhaust air. This is what is done in a vacuum cleaner.
The electric pump as it is called (which means a pump worked by an
electric motor), exhausts some of the air from a compartment in the
machine, and the atmosphere pressing in through nozzle and hose carries
dust from rugs and furniture with it into the compartment. The best vacuum
cleaners will produce a pressure of seven or eight pounds per square inch,
about half an atmosphere. This will remove dust from the warp and woof of
a rug better than our greatest hurricanes can when the rugs are hung upon a
line. There are three kinds of air pumps in use with vacuum cleaners: (1)
bellows, (2) rotating disk or fan, (3) piston.
To milk cows by electricity is simply to apply the vacuum-cleaner idea to
the process, and, in general, doing things by electricity usually means doing
them by some machine that is made to go by an electric motor. This then is
the first key to the Electrical Show, and if you will remember to look first
for the motor it may remove much of the mystery from some of the
exhibits. In many cases it is not necessary to have a complete electric motor,
but simply an electro-magnet to do the work. In booth No. 56 you will find
a piano played by electricity. Its keys are moving, but no hands strike them.
There is no ghost at work here. A little strip of iron has been placed upon
the under side of each key and a small electro-magnet is placed under that.

It is only necessary that wires should run from these electro-magnets to two
dry-battery cells and to push buttons, and a person far away may play the
piano. In reality, however, it is not a person but a roll of punctured paper
that opens and closes the electric circuits to these various magnets
underneath the keys.
It often happens that you see a person playing a pipe organ with his
keyboard far removed from the organ itself. In this case the keys simply act
as push buttons to close the electric circuit through electro-magnets placed
in the organ itself. These electro-magnets operate the air valves of the
various pipes.
You call at some apartment house where there is
no hall boy, but a row of push buttons labelled
with the names of the tenants. You push a button
and the door which was locked opens apparently
of its own accord. To say that the door opens by
electricity is only to add mystery. What does
happen is that an electric bell up in the
apartment rings in response to your push of the
button, and in reply the tenant pushes a button
and the door is unlatched by an electro-magnet
concealed in the door casing (Fig. 25).
So I would say that the first key to the Electric
Show or to the multitude of electrical appliances
which you meet in life is the electro-magnet.
Consider the motor as one illustration of its use.
If you are really to understand the Electric Show
you should go twice. I advise going with this Fig. 25
key alone first and note down all the
applications of electro-magnets which you can find there. When you have
done so I shall be glad to have your report.

VI

APPLICATIONS OF THE ELECTRO-MAGNET
t became quite the rage now among the boys to find as many uses of

I electro-magnets as possible. These were reported and explained to the
club and a list kept. This list included:
1. Dynamo.
2. Magneto.
3. Ammeter.
4. Wattmeter.
5. Motor.
6. Electric piano and organ players.
7. Electric door openers.

Already noticed in the preceding pages, and the following:
8. The Electric Spinner (Fig. 26).—A toy
full of instruction. The standard is a steel
magnet which produces a magnetic field.
Inside of this is an electro-magnet which
serves as an armature. Plainly visible on its
shaft is a commutator to which the electric
current from a dry cell is sent. This causes
the armature to revolve and carry with it a
series of colour disks which may be
adjusted so as to show what tint or shade
results from mixing colours in various
Fig. 26 proportions.

Fig. 27

9. The Electric Engine (Fig. 27).—This
toy, with one dry battery cell, develops
power enough to run several other toy
machines. The diagram in Fig. 28 will
make its plan of operation plain. B is the
battery cell, c the electro-magnets, a an
armature of iron. By a rod this armature is
connected with a crank on the axle which
carries the fly wheel f. Another crank, d,
upon the same axle serves like a push
button to close the electric circuit at the
right instant. The wire g from the battery
cell encircles the electro-magnet c and
then is connected to the iron base of the
toy. When the crank d touches the
conductor e, which is a spring, the electric
current passes around the magnet, the
Fig. 28 magnet pulls the iron armature a, and this
gives an impulse to the wheel f whose
momentum carries it around during that portion of the revolution when d is
separated from e and a is receding from the magnet.

It is customary to say that the circuit is closed through the base of the
machine, but this language requires interpretation. It means that a way is
provided for the electric current to pass through the base. A person who is
expert in language but not in electricity might expect us to say "the circuit is
open through the base."
10. The Telegraph Sounder (Fig. 29).—
This was a toy half a century ago, but
since the days of Samuel Finley Breese
Morse it has become of vast commercial
importance. The Western Union Telegraph
Company in 1909 had 211,513 miles of
poles and cables, 1,382,500 miles of wire,
24,321 offices, sent 68,053,439 messages,
received $30,541,072.55, expended
$23,193,965.66, and had $7,347,106.89 in Fig. 29
profits. In the United States more than
93,000,000 and in the world at large more than 600,000,000 messages are
sent annually, and there are men still living who scoffed at Morse's ideas as
impracticable.
It is interesting to contemplate what would happen to the Stock Exchange,
to the newspapers, to the railroads, to the congressman addressing his
constituents from the floor of a legislative chamber, to business in general,
if the world were deprived of the telegraph.
A few years ago a telegraph despatch was sent from New York to San
Francisco, Tokio, London, and back to New York, 42,872 miles, in three
minutes less than an hour. Electricity can travel around the world in a
fraction of a second, the time was consumed in repeating the message. I
once sent a message from New York to New Haven to announce that I was
coming, and afterward took my train and reached New Haven in time to
receive my own message and pay the messenger boy. But I have never lost
faith in the beneficent results of Morse's labours.
Morse (1791–1872) was an artist and the first President of the National
Academy of Design. He was likewise a professor in New York University
and constructed his first experimental telegraph line upon the University
campus in 1835. His first public line was built from Washington to

Baltimore in 1844. The Western Union Telegraph Company was
incorporated in 1856. Of course the work of Morse rested upon that of
Oersted, in Copenhagen, who, in 1819, discovered electro-magnetism, and
upon that of Joseph Henry of Albany, who in 1827 first insulated the wires.

Fig. 30

The application of the electro-magnet to producing telegraphic signals will
be understood by referring to Fig. 30. B is the generator of an electric
current—sometimes a battery and sometimes a dynamo. One wire from this
goes to the earth, E. The other wire goes through a key, which, like a push
button or a switch, serves to open or close the circuit. This is normally
closed when not in use. Through this the current passes around the electro-
magnet S, which attracts the armature a, causing it to click against a metal
stop, hence it is called the sounder. From this the current passes along the
line wire to a distant station and there through the sounder and closed key to
the earth. There is likely to be a generator at each station. The current must
run continually through the system. If a battery is employed, the copper
sulphate, or gravity cell, to be described later, is chosen, because it will
endure continued usage better than any other.
The operator, in sending signals, opens the circuit, the magnets cease to
hold down the armatures, and they are raised by springs and strike against
metallic stops above. It is customary to say that the circuit is completed
through the earth. This statement misleads some persons into imagining an
electric current capable of corroding water pipes and decomposing chemical
compounds, passing through the earth between stations.

Photograph by Helen W. Cooke
Testing the Telegraphy Outfit

Perhaps it will help to a better understanding of the truth if we think of a
city pumping water out of the ocean, say to fight fire, and disposing of it
again into the ocean. The ocean currents thus produced are not likely to be
destructive. Indeed, just as we measure height from the ocean level as zero,
so we measure electric pressures as from the zero level of the earth's
electrical state.
The key used by telegraphers is represented in
Fig. 31. It has connected with it a switch to keep
the circuit closed when the key is not in
operation. The Morse code of signals consists of
dots and dashes, when printed, as follows:
a .- Fig. 31
b -...
c .. .
etc.
Operators learn to read the message by the intervals between sounds. A dot
consists of two taps of the sounder with a short interval between, and a dash
consists of two taps with a longer interval between. One tap of the sounder
is caused by its descending upon the metal stop below and another by its
rising against the upper stop.
Telegraph sounders are operated on about a quarter of an ampere of current
if from a battery circuit, or on about one tenth of an ampere from a dynamo
circuit. The dynamo circuit is supplied with more volts of electric pressure,
and hence its power is ample to cause the armature to strike the metal stops
hard enough to be heard by the operator.
For example a battery circuit may supply to the sounder a current with these
characteristics:
2 volts × .25 amperes = .5 watts,
while a dynamo circuit may give:
6 volts × .1 ampere = .6 watts.
Telegraph line wires are usually bare, the insulation being merely the glass
knobs at the poles. Clean water is a very good insulator but dirty water is a
fairly good conductor. A wet telegraph pole may bring so much current to

earth as to prevent all sounders on the line from operating. Hence the line is
separated from the poles by glass. The poles are about one hundred and
thirty-two feet apart, making forty to the mile. The wires are usually
galvanized iron one sixth of an inch in diameter. Copper conducts six times
as well as iron, and is now replacing iron in the lines.
Morse laid a submarine telegraph line in New York Harbour and suggested
a cable across the ocean. But that gigantic undertaking had to await the
masterful intelligence of Lord Kelvin and the indomitable will of Cyrus W.
Field. A submarine cable was laid across the Strait of Dover in 1850. It was
cut by the anchor of a fisherman a few hours after it was laid. The first
attempt to lay a submarine cable across the Atlantic Ocean was made in
1857. Two ships of war, the Agamemnon of Great Britain and the Niagara
of the United States, engaged in this undertaking. Three hundred miles had
been laid when the cable parted where the ocean was more than two miles
deep. William Thomson was on board the Agamemnon as electrical expert.
He went home to study and improve the methods. The next year, 1858, the
Agamemnon and the Niagara met in midocean each with a portion of the
cable on board. The splice was made, and the Agamemnon started toward
Ireland and the Niagara toward Newfoundland. When six miles apart the
cable broke. The ships met again, made a new splice and again started in
opposite directions. They laid eighty miles and the cable parted a second
time. They met again, spliced and laid two hundred miles when it parted for
the third time. They met a fourth time, made the splice and succeeded in
laying the first cable from Ireland to Newfoundland on August 5, 1858.
In a few weeks the insulation failed and no more messages could be sent.
Seven years were spent in studying the problem, and again in 1865 the
Great Eastern, a mammoth ship, started to lay the cable. William Thomson
was again on board as the expert. When twelve hundred miles had been laid
the cable parted in deep water. Three times the cable was grappled and
brought part way to the surface and lost again. The Great Eastern returned
to land. The next year, 1866, the Great Eastern, having on board William
Thomson (Lord Kelvin), Mr. Canning, the engineer of the expedition, and
Captain Anderson, in command, laid the cable which has worked
successfully ever since. Thomson, Canning, and Anderson were knighted as
a result of their labours. Sir William Thomson (1824–1907), afterward Lord
Kelvin, is credited with having solved the difficult electrical problems

connected with this enterprise. Cyrus W. Field (1819–1892), born in
Stockbridge, Mass., helped to secure the many millions of dollars necessary
to carry the work to completion.
There are now seventy-three cables connecting Europe and America, and
two across the Pacific Ocean. Cable rates are: New York to England,
France, Germany, or Holland twenty-five cents a word, to Switzerland
thirty cents a word, and to Japan one dollar and thirty-three cents a word.
The boys were kept very busy now looking up historical and biographical
sketches, as well as working up the many applications of the electro-
magnet. The next to be reported was:

Fig. 32

11. The Relay (Fig. 32).—Telegraphing from 3,000 to 10,000 miles under
the ocean is full of difficulties not now to be explained.

Fig. 33

Of course when we attempt to telegraph many miles upon land we find that
the resistance of the wire cuts down the strength of the current so that it will
not move the sounder. This, however, is readily obviated by the relay
devised by Morse. It simply serves as an automatic key to close a circuit. A
diagram will make this clear (Fig. 33). Suppose the line wire to be very

long and on account of its resistance the current is too feeble to operate a
sounder. It is likely to be about .025 ampere where the local sounder may
require .25 ampere or ten times as much. It is easily possible to wind a
magnet (Fig. 33), R, such that .025 ampere will close the armature a, so that
it may complete a local circuit when it would not make noise enough for a
sounder. B may represent a local battery of any desired strength which may
operate the sounder S of that station as loudly as may be desired.

Fig. 34

12. Annunciator (Fig. 34).—We live in a fifth-floor apartment. When we
push the button to call the elevator a No. 5 appears in the annunciator in the
elevator car. This tells the elevator boy where the call comes from. Take out
two or three screws and the annunciator opens, revealing a series of electro-
magnets like the one shown in Fig. 35. When an electric current passes
around the coil it pulls back an iron catch and allows a number to drop so as
to show through a small window. The elevator boy, having noted that the
call is from the fifth floor, pushes up the number and the iron catch holds it
until the coil is magnetized again by an electric current.
The annunciator has a bell to call attention. A cable of six wires enters this
annunciator (Fig. 36). One wire goes direct to the bell and the other five

reach the
bell
through
the
separate
coils of
the
electro-
magnets
which
control
the drops. Fig. 35
But how
are electrical connections made between a
moving elevator car and the push buttons
on various floors? The diagram in Fig. 37
Fig. 36 shows this in elevation. B represents a
battery of several dry cells located in the
basement. One wire from it runs direct to
the push buttons 1, 2, 3, 4, 5, located upon the five floors of the house. The
other wire from the battery, together with wires from each of the five push
buttons, all run to a point, A, half-way up the elevator shaft. Here the six
wires are gathered into a cable long enough to reach either to the top or the
bottom of the elevator shaft. The other end of this cable enters the elevator
car and runs to the annunciator. The wire from the battery goes direct to the
bell. The wires from the various push buttons go through correspondingly
numbered electro-magnets to the bell. When, therefore, we pushed the
button on the fifth floor, we closed the gap in the electric circuit at that
point. The current came up from the battery, passed through the button,
went down the cable to the car, went through electro-magnet No. 5, went
through the bell, and returned direct to the battery, thus completing the
circuit. Annunciators are used about buildings to call other attendants,
besides the elevator boy. They are likewise used in burglar alarms to inform
the householder which door or window is being forced. They are used in the
fire department to tell what part of the city the call came from.

Fig. 37

Fig. 38

13. The Electric Bell and Buzzer (Fig. 38).—So common a thing as an
electric bell really belongs to the present generation. Bells were either
novelties or toys when I was your age. They cost then many times what
they do now and then were poorly made. Nobody dared to trust them for
front-door bells. It was necessary to have a card permanently posted over
the push button saying, "If the bell does not ring, knock." In those days
batteries were troublesome to care for, houses were not wired when built,
and no one had learned the art of concealing the wires neatly.
The buzzer is simply a bell minus gong and hammer. Those shown in Fig.
38 ring well on a single dry cell. A cell costing twelve cents operated one
for two years while it was used as a call bell from dining room to kitchen,
the current required being .15 ampere.

Fig. 39

Electric Bell

The connections are shown in the diagram (Fig. 39). Suppose the current to
enter at the binding post a, pass around the magnets b and then to the post c.
The armature d normally rests against the post c and the current finds its
way along this to the post e and thence back to the battery. But as soon as
the current passes, b becomes a magnet and pulls the armature d away from
the post c, thus breaking the circuit, when b ceases to be a magnet and a
spring pushes the armature d back against the post c to repeat the operation.
The armature d carries a hammer which strikes the gong f. If the wire,

which is usually connected with the binding post e, is connected with the
post c, the "clatter" bell is changed to a "single-stroke" bell, and if the gong
and hammer are removed the "bell" is changed to a "buzzer."
In the case of the buzzer, by changing the
length of the armature or by weighting it,
we may change the time of its vibrations
and its tone. The connections between
battery push button and bell form a Fig. 40
complete circuit. In Fig. 40 B represents a
battery, usually of dry cells, B' represents the bell, and P represents the push
button. The electric circuit is "open," (that is, there is a break in the
conductor) at P until some one "pushes the button," that is, simply pushes
against a spring so as to cause a piece of metal to bridge the gap in the
conductor. Then we say the circuit is "closed."

Fig. 41

Fig. 42

Push button devices and switches are innumerable. In every case they are
simply devices for pushing one piece of metal against another and
completing the circuit for an electric current. Every one should unscrew and
examine a few of them, both for the pleasure of seeing how they work and
to learn how to make them work when they sometimes fail. Not only in
bells but in all other instruments where electro-magnets are used, the
magnets are placed in pairs, fastened together upon an iron base. They are
wound so that the free ends are made opposite poles by the electric current.
Like a horseshoe magnet, they form one magnet. The two poles thus placed
are mutually helpful and each is stronger than it would be if separated from
the other.

Fig. 43

14. Electric Clocks, Self-winding Clocks, Programme Clocks.—A
pretentious-looking thing which appeared like a dish pan with a glass
bottom was opened by the boys and found to be the simplest of all clocks. It
had an electro-magnet like that in Fig. 44. A strip of iron acting as an
armature across the free ends of this magnet, pushed like a finger against
the cogs of a wheel. This wheel was on the axle of the minute hand and it
had sixty cogs. The electric circuit was closed through the magnet for an
instant each minute and the armature pushed the wheel ahead one cog. Thus
it made one complete revolution in an hour. A train of four other cog-wheels
caused the hour hand to trail after at one twelfth the speed of the minute
hand. This machinery made simply a small handful in an eighteen-inch
stamped-metal "dish-pan" costing fifteen dollars.
A self-winding clock was opened and found to contain two dry battery cells,
an electro-magnet which operated very much like that of a "clatter" bell, the
hammer like a finger poking against the cogs of a wheel. Once an hour the
long hand closed the circuit through the battery and the magnet and its
armature swung back and forth long enough to give the cog wheel one

complete revolution and wind a spring,
which it carried upon its axle. This spring
kept the clock running one hour, until the
next winding.
The programme clocks which were
examined were self-winding clocks, but
were connected by wires to the master
clock which corrected them each hour.
Fig. 44 Each time the long hand of the master
clock came to twelve it closed an electric
circuit through all the clocks in the system. In each clock the current passed
around an electro-magnet and caused it to pull an armature against a metal
stop and set each long hand exactly at twelve. This master clock is
sometimes situated many miles away and may correct the time for a whole
city. Thus a master clock at Washington, D. C., furnishes standard time to
all parts of the United States. The master clock which we examined also
closed the circuit at proper intervals through a series of programme bells
placed in the various class rooms, and these called and dismissed classes
automatically.

Fig. 45

15. Watchman's Time Detector (Fig. 45).—This is a device to compel a
watchman to make his appointed trips. Push buttons or switches are
distributed about the building at various points, and it is made his duty to
close the circuits at these points at stated times. When he does so, the fact is
recorded by electro-magnets puncturing, or, in some way, marking a
revolving time card in the clock.
16. Circuit Breakers (Fig. 46).—Electro-magnets are used to open switches
and thus protect dynamos and other machines against a larger electric
current than they are able to carry. The switch is held closed by a spring

which, by an adjusting device, may be
tightened or loosened. A dynamo which we
examined had its circuit breaker adjusted
so that it would remain closed if any
current under 1500 amperes passed, but if
a greater current than that passed it would
strengthen the magnet sufficiently to open
the switch and thus break the circuit.
17.
Separatin
g Iron
from Ore.
—In 1897
Edison
Fig. 46 first
proposed
to use an electro-magnet to separate iron
from crushed earth. Fig. 47 represents the
process. E is an electro-magnet. S is the
stream of crushed ore containing iron.
Gravity would cause all the material to fall Fig. 47
into bin A, but the electro-magnet E pulls
that portion of the material which is
magnetic to one side so that it falls into the bin B.

Fig. 48

18. Lifting Magnets.—Electro-magnets are made for use with hoisting
apparatus to save the trouble of manipulating grappling hooks, etc. They
may lift barrels and boxes of iron, the wood of the barrel or box being
transparent, we say, to the magnetic influence. That is, the magnet will
attract iron through the wood just as light will shine through glass. Such
magnets are used to pick up from the bottom of the sea cases of hardware
from wrecked ships. (See the accompanying illustration, Fig. 48.) In such
cases the electric conductors which lead to and encircle the magnets must

be well insulated from the water of the sea, otherwise the electric current
would take the shorter path from one line wire through the sea water, which
is a fairly good conductor, and back by the other line wire, rather than go
the path of greater resistance around the magnet. Electro-magnets are
coming into use in foundries, etc., for lifting heavy iron castings.
19. Electro-Magnet on Starting Box.—As
was explained under electric motors, a
starting box is simply a series of resistance
coils r, r, r, r, r, in Fig. 49. When the
motor is not in use the switch l rests upon
the point 1 and no electric current passes.
When the switch is moved to point 2, the
current entering at a passes to the pivot of
the switch and up the metal strip l to the
point 2, then around the series of coils, r, r,
r, r, r, to the post b and thence back to the
generator. As the switch is moved to the
right, the current passes through less and
Fig. 49
less of this resistance until, when it reaches
point 7, all the coils of resistance are "cut
out," that is, they are not in the path of the current. Now the motor has
reached its full speed and is developing enough counter-electro-motive
force to protect itself against too much current. Through a shunt, however, a
portion of the current passes from a to b around the electro-magnet e, the
two poles of which are presented to the metal strip l, which must be of iron.
This magnet holds the switch over so long as the current is on, but when the
current is cut off, by opening a switch in the line wire, e ceases to be a
magnet and l is carried back to point 1 by a spring. Thus an extra resistance
must always be in circuit when the motor is first started. Those who start
motors are expected to move the lever l of the starting box slowly from
point to point, pausing a second or two on each to give the motor time to
acquire proper speed for its protection. How too great a current would "burn
out" a motor will be explained later.
The motor man handles a lever for starting his car, which works like that of
the "starting box." His "starting box," however, is called a "controller."

Although it accomplishes the same result as the starting box it has a wholly
different and vastly more complex mechanism than that already described.
The elevator boy, who runs our electric elevator, handles a lever which also
does the same thing through far different mechanism. Indeed, in his case
electro-magnets are used to prevent him from cutting out resistance too fast
if he should move his lever too quickly.
20. Starting Switches for Electric Elevators.—The motor man has to be
instructed particularly how he should handle the lever of his controller, and
he is trusted to follow his directions to some extent, however lacking in
intelligence and integrity he may be. But the elevator boy receives scarcely
any instructions about his machine, and, indeed, his machine has been
constructed pretty nearly "foolproof." It will automatically correct his errors
of management. If he throws the handle from one extreme to the other, all
resistance cannot be thrown out instantly, but this is accomplished by a
series of electro-magnets closing one switch after another and thus cutting
out resistance gradually.
21. Arc Lamp Feed.—As will be explained later, an arc lamp must have its
carbons touching one another when the current is first thrown on, and then
the carbons must be drawn apart from a quarter to half an inch. The upper
carbon is lifted away from the lower one by a portion of the current passing
by means of a shunt around an electro-magnet.

Fig. 50

22. Volt meter.—The volt meter measures
the pressure of an electric current. The volt
meter which we examined looked outside
like our ammeter, and when we removed
the face it appeared inside like an
ammeter. There was the steel magnet of
horseshoe shape to furnish a field (Fig.
51), and there was an electro-magnet
poised between its poles for an armature.
The armature in the volt meter, however,
had wound upon it finer wire and more of
it than was the case in the ammeter. There Fig. 51
was no shunt wire in the volt meter as
there was in the ammeter. We connected in
series a fluid cell (to be described later),
the ammeter, and the volt meter (Fig. 52).
The ammeter shunt was removed so that
all the current went through its armature.
The volt meter needle went to one which
was two thirds of the scale (Fig. 53), and
the ammeter needle indicated .016. That is,
this particular cell can push sixteen
thousandths of an ampere through the
resistance of this volt meter, and .016
ampere passing through the armature of
this volt meter will magnetize it
sufficiently to move it against its spring, Fig. 52
say sixty degrees.

Fig. 53

We put into the circuit a lot more fine wire
for resistance, R (Fig. 54), so that the volt
meter needle went only half as far as
before, that is to .5. The ammeter indicated
only half as much as before, that is .008
ampere. We put in resistance enough to
bring the volt meter needle down to .25
and the ammeter indicated one quarter of
the original current. We put in less
resistance, bringing the volt meter needle
to .75, and the ammeter indicated three
Fig. 54 fourths of the original current. Evidently
the volt meter is merely an ammeter with a
different scale marked upon its card. With a pen we marked upon the card
of the volt meter a true ammeter scale (Fig. 55).

Fig. 55

In order to understand the volt meter, let us turn our attention for a moment
to Fig. 56. I have arranged the water tank T at such a height above the
faucet F that when the faucet is opened one quart of water will flow in a
minute. If I partially close the faucet, making the opening one half as large
(that is, offering twice the resistance to the flow), half a quart will flow in a
minute. If I make the resistance four times as great only one quarter of a
quart will flow in a minute. It is evident that I could arrange a scale
underneath the handle of the faucet to indicate the quantity of water

flowing, just as the ammeter and volt meter
indicate the quantity of electricity which flows.
If now that much is understood, it will be easy
to learn how the water faucet may be used to
measure water pressure and the volt meter in
like manner used to measure electric pressure.
Having set the faucet so that a quart will flow
per minute, let us put on a longer tube p, and
move the tank up to another shelf so that the
distance from the water level in the tank to the
faucet is twice as great as before. Under the
increased pressure water runs through the faucet
twice as fast and we now get two quarts per
minute.
I purposely placed the tank out of sight behind a
partition so that you might practise judging the
water pressure by the flow at the faucet. We
cannot very well talk about pressure in quarts.
We might talk about it in pounds, but if we used
this apparatus much we should probably get into
the habit of talking about the pressure from one
shelf, two shelves, three shelves, etc.
In order that the pressure might remain nearly Fig. 56
constant during the experiment we would
probably introduce resistance (that is, partially close the faucet) so that the
water level should not fall much. We might, for example, set the faucet so
that half a pint would flow in a minute when the tank was on the first shelf.
Then a pint per minute would flow when the tank was on the second shelf
and one and a half pints per minute when the tank was on the third shelf,
etc. Thus we should infer the pressure by measuring the quantity.
One more illustration and the case will be clear. To save the trouble of
measuring the quantity of water which flows through the faucet, suppose I
introduce the device represented in Fig. 57. W is a small water wheel
comparable to the armature of the volt meter. It carries a pointer which
moves over a scale just as in the case of the volt meter.

It has a spring coiled around its axle which
tends to keep the pointer at 0, as in the
case of the volt meter. The tank is placed
upon the first shelf, the faucet is fixed so
that a small amount of water flows and the
needle moves to a certain figure upon the
scale. We will mark this point one and call
it "first-shelf pressure." The tank is lifted
to the second shelf and the index moves to
another point, which we will mark two and
call it "second-shelf pressure." The tank is
lifted to the third shelf and the index
moves to a third point, which we will mark
three and call it "third-shelf pressure," etc.
Ordinarily we measure water pressure with
an instrument which allows no water to Fig. 57
run to waste, but in measuring electric
pressure by the volt meter some current
must pass through the instrument, just as in the case of our water-wheel
illustration in Fig. 57. We put in large resistance so as to make this current
as small as possible, while we let enough pass to move the armature.
Now let us return to the volt meter itself.
By referring to Fig. 55, we see that it
requires .024 ampere to move the needle
of the volt meter clear across the scale, and
we have found that one fluid cell was able
to send enough current through the
resistance of the armature to move the
needle two thirds of the way across the
scale. At this point we find Fig. 1, which
might be read "one-cell pressure." We
Fig. 58 prefer to commemorate the name of one of
the workers in the field of electricity and
call this pressure a "volt" after Alessandro Volta (1745–1827), born at
Como, Italy. It is the electric pressure which is produced by one fluid cell of
a certain kind. We say, then, that one volt pushes through the resistance of

this armature .016 ampere. Half a volt would push through the resistance of
the armature half as much current or .008 ampere. At this point we put .5.
Thus each of the figures in the lower row (Fig. 55) shows what part of a
volt is required to send enough current through this particular armature to
move the needle to that point.
We found out how much wire was wound
upon the armature and put exactly the
same amount in the outside resistance, R
(Fig. 59). The needle now showed that one
volt is able to push through twice the
resistance of the armature only half as
much current, and the needle stopped at
.008 ampere. If this were to be the
resistance in the volt meter circuit one volt
should stand under .008 ampere and two
under .016 and three under .024. It is Fig. 59
evident then, that, if we know the internal
resistance of a volt meter, we may make it
capable of measuring greater electrical pressures by adding the proper
amount of resistance. By putting at R, (Fig. 59) nine times the internal
resistance of the instrument, thus multiplying the total resistance tenfold,
the figures upon the scale of volts may be read as whole numbers from one
to fifteen. In this case it will require fifteen cells to push the needle clear
across the scale and ten cells to push it two thirds of the way across. If now
we add enough external resistance to multiply the resistance of the armature
a hundred fold it will require 150 volts to push .024 of an ampere through
the armature and pull its needle clear across the scale. In this case the
figures upon the scale of volts are multiplied by one hundred and read from
ten to one hundred and fifty. Such a scale would adapt this volt meter for
use with our 110-volt lighting circuit. Volt meters are made with a series of
such external resistances, called "multipliers," attached so that they may be
easily thrown into the circuit.
It is evident that we need some term so that we may speak of quantities of
resistance. This need has given rise to a unit of resistance called an ohm,
after George Simon Ohm (1789–1854) born at Erlanger in Bavaria. Two
inches of No. 36 German silver wire, such as is wound upon the armature of

this volt meter, gives one ohm of resistance. There are 125 inches of this
wire upon the armature. Its resistance is, therefore, 62.5 ohms, and we may,
therefore, say that one volt of electric pressure can push through 62.5 ohms
of resistance .016 of an ampere of current. Ohm discovered this relationship
in 1827, and formulated it as follows:
volts/ohms = amperes (not, however, using these words).

(1 volt)/(62.5 ohms) = .016 ampere.
62.5) 1.0000 (.016
625
——
3750
3750
——

This is called Ohm's law, as every candidate for college admission will hear
and hear again.
Volt meters and armatures for the
alternating current have electro-magnets
for their fields as well as for their
armatures. Such instruments are equally
well adapted for either direct or alternating
currents. For when the current reverses its
direction it reverses in field and armature
alike, and thus a repulsion between like
poles is maintained. Such an instrument,
however, cannot respond to as slight a
current as those previously described,
since they must consume some energy in
both field and armature. Fig. 60

23. Telephone Receiver (Fig. 61).—It
requires a stretch neither of the
imagination nor of the truth to call a
telephone receiver an electro-magnet,
although perhaps it has never been called
that before. We took it apart and found that
Fig. 61
it consisted of a steel-bar magnet m (Fig.
62), with a small spool of wire w around
one end of it. The ends of the wire on the spool run along inside the hard
rubber shell to the two binding posts a and b at the other end. A disk of
sheet iron S is held in the large end of the case very near to, but not quite
touching, the end of the magnet. When an alternating current is sent through
the wire upon the spool it causes rapid changes in the strength of the
magnetic field, if not reversals of the poles of the field, and the iron disk is
made to vibrate, keeping time with the alternations of the current.
In this laboratory we have seen that our
current has sixty alternations per second.
When it is connected with the receiver the
disk, therefore, makes sixty vibrations per
second, and produces a tone which has
very nearly the pitch of C two octaves
below the middle C upon the piano.
Fig. 62
24. Spark Coil (Fig. 63).—The automobile
spark coil which we have already used is
an electro-magnet. The battery sends a current through wire coiled around
an iron core. At one end of this iron core is an iron armature which is made
to vibrate in precisely the same manner as the armature of an electric bell.
This makes and breaks the current and causes rapid changes in the strength
of the field. A rapidly changing magnetic field may be used to develop
electricity in a conductor, as we have already seen in the case of the
dynamo.
How it is used in the automobile spark coil will be shown later. It is
sufficient now to mention it as a case of a magnetic field produced by an
electric current passing through a wire coiled around an iron core, or, in
short, an electro-magnet.

Induction coils, Ruhmkorff coils, and
transformers, to be described later, are
closely related to this. They all create
magnetic fields in the same way and are all
electro-magnets.

Fig. 63

Fig. 64. Transformers

VII

ELECTRIC HEATING
t was Washington's birthday. The schools were to have a holiday and the

I Science Club was to hold a special, open meeting at which I had been
asked to present the subject of electricity in the household. I replied to
the programme committee that that was too large a subject, but that I would
talk upon electric heating. I warned them, however, that it would be a dry
study, and not an entertainment. They replied that the father of his country
had been born at a time of the year when the weather was unfavourable to
outdoor sports, and that February usually found them acclimated to
vigorous study. Neither they nor their friends objected to study if it seemed
to have a motive.
I found an audience composed of old and young, men and women, girls and
boys. Most of them had left school—many of them because their teachers
thought they were incompetent to continue.

Fig. 65

Not far from here is "a wheel in the middle of a wheel ... as for their rings
they are so high that they are dreadful ... and the spirit of the living creature
is in the wheels." Those wheels are now sending the electric current to this
room for our experiments. I propose to show that we convert electricity into
heat by offering resistance to its flow. Experience teaches us that resistance
to motion always produces heat. At Niagara Falls thousands of tons of water

descend at the rate of one hundred and sixty feet in three seconds. When the
water reaches the bottom of the falls, it is moving a little faster than a mile a
minute. The resistance which this mass meets after its fall retards its motion
and generates heat.
Hundreds of meteors fall into our atmosphere daily, travelling a thousand
times as fast as the waters of Niagara Falls. The resistance to their motion,
which our atmosphere offers, heats them white hot, melts them, vaporizes
them, burns them up, so that very few of them reach the solid earth in a
solid condition.
An iron spile driver, measuring two cubic feet, weighs about half a ton.
When it falls sixteen feet upon the end of a spile it is moving at the rate of
twenty miles an hour. The energy of this moving mass depends upon both
its weight and its velocity, and when its motion is arrested by the spile that
energy of motion is largely converted into heat energy, from which both the
spile and the spile driver get hot.
A piece of iron may be made red hot by pounding it with a trip hammer.
Count Rumford found, in 1798, while boring cannon in the arsenal at
Munich, that the resistance which the iron offered to the motion of the
boring tool furnished heat enough to boil water.
Seven hundred and seventy-eight foot pounds of mechanical energy when
converted into heat would raise one pound of water (one pint) one degree.
This is called the British thermal unit. The spile driver, weighing 1000
pounds, falling 16 feet upon a spile, produces heat enough to raise 1 pint of
water 20 degrees.

Fig. 66

Here are two binding posts, a and b, 8 feet apart (Fig. 66), connected by
copper wires with the dynamo circuit. The volt meter indicates 112 volts of
pressure. I will close the circuit by stretching between a and b 8 feet of No.
24 iron wire. (This wire is about the thickness of a common pin.) The iron
wire offers resistance to the flow of the electric current, thereby producing
heat—heat enough as you see to make the wire white hot, indeed heat
enough to raise it to something over two thousand degrees Fahr., for now
you see it has melted.
We will put in a fresh piece of wire and connect also the ammeter in the
circuit (Fig. 67). As I close the circuit the needle of the ammeter at first
indicates 20 or 30 amperes, but in a second drops to 8 amperes, and remains
there a second until the wire melts and falls apart. One hundred and twelve
volts of electric pressure are able to push 8 amperes of electricity through
this wire when hot.

Fig. 67

(112 volts)/(14 ohms) = 8 amperes

112 volts × 8 amperes = 896 watts

746 watts = one horse-power

Hence it required about one and one fifth horse-power to melt the wire in a
second, and the heat produced was a little less than one British thermal unit,
a unit much used by engineers.
1 pound raised 1 foot = 1 foot pound
550 foot pounds per second = 1 horse-power

778 foot pounds (1.4 H.-P.) = 1 B. T. U. (British thermal unit) = heat required to raise
1 pound of water 1° Fahrenheit
1 volt × 1 ampere = 1 watt
746 watts = 1 horse-power

In order to hold back 112 volts of electric pressure so that not more than
eight amperes of electricity should pass, the iron wire must have offered
about 14 ohms of resistance.
The behaviour of the ammeter needle showed that the wire offered very
much less resistance when cold than when hot. Indeed eight feet of No. 24
iron wire offers about one and one third ohms resistance when cold, hence
heat had increased its resistance to the passage of the electric current
tenfold.
This piece of iron wire offered resistance to the flow of the electric current.
It offered resistance to the motion of the dynamo. This offered resistance to
the steam-engine which drives the dynamo. This caused the governor of the
engine to open and pass more steam from the boiler. This reduced the
pressure at the steam gauge. This caused the fireman to shovel more coal
into the furnace. The heat of the burning coal melts the wire, but it does it
only after several changes. First, it is converted into mechanical energy in
the steam-engine with great loss—about nine tenths being lost. Second, it is
converted into electrical energy by the dynamo, with some loss, and, third,
it is conducted to the iron wire and converted back to heat with still further
loss. It is evident that the most economical way to heat the wire would be to
take it to the furnace. Yet all electric cooking is done by sending electric
current through wires embedded in the walls of the cooking utensils, and it
is the most wasteful method of using the energy stored in coal that has yet
been devised.

Fig. 68

That merely connecting the binding posts a and b (Fig. 67) by a small piece
of wire should throw a load upon the dynamo miles away; should offer
resistance to its motion, and make it require 1.18 horse-power more of
energy to keep up its speed of revolution, is, indeed, uncanny. I will attempt
to make it seem more real. At one end of the lecture table I have a rotary
pump P (Fig. 68). The end of the rubber tube a, which leads to the pump is
lying upon the table outside of the tank of water, T. While things are in this
condition I move the crank which operates the pump with perfect ease. Now
while still turning the crank I pick up the tube a and drop its free end into
the water tank. I cannot now conceal the fact, even if I were disposed to do
so, that I must work hard to keep the pump going. The pump itself tells you
by its laboured sound that it is working hard, and the stream of water which
issues from the pipe b tells how much work I am performing. The pump is
discharging five and a half pints of water per second, that is 5.5 pounds, and
it raises this water 10 feet. Hence I am doing 55 foot pounds of work per
second, which requires one tenth of a horse-power. Here is a lad who
consents to try the experiment for us. He turns the crank easily while I am
holding the tube a out of the water, but when I lower it into the water he

finds the resistance so great that, tug however much he may, he is unable to
keep the pump going.
At the other end of the table I have a small hand dynamo, D (Fig. 68), M is
an ammeter, V is a volt meter, S is a switch. All the wires are good-sized
copper, and offer little resistance, except that stretched between the binding
posts a and b. This is a piece of fine German silver wire. While the switch is
open I turn the crank of the dynamo with perfect ease. A small amount of
current is going through the volt meter, but this is too slight to offer any
perceptible resistance to the motion of the machine.
Notice that the volt meter needle moves according to the speed of
revolution. If I turn the crank once a second the needle stands at 25 volts.
The electric pressure increases or decreases according to whether I rotate
the armature faster or slower. Now I will attempt to keep the machine
revolving at a constant rate while I close the switch S, and surely you must
see that I have hard work to do so. The wire a b has now become red hot.
The volt meter shows 25 volts of pressure, and the ammeter shows 3
amperes of current.
Twenty-five volts × 3 amperes = 75 watts, which require one tenth of a
horse-power (746 watts = 1 horse-power). The lad now takes my place at
turning the machine and finds it easy when the switch is open, but I actually
overload him by merely closing the switch. Heating the wire red hot
requires more energy than he is able to put forth.
I proposed to the president that my lecture close at this point, and that each
one in the room have a chance to feel the load which was thrown upon the
dynamo each time it was required to heat the wire. I suggested that each
person should get a realizing sense of this fact, first by doing the work
himself, and second by going home and reflecting upon this hint. When the
switch is closed three amperes of electricity pass around the circuit. This
increases the magnetism in both the field and the armature of the dynamo,
and it requires one tenth of a horse-power more to keep the armature
moving within the field against this magnetic pull.
I further desired to announce that during this hour I had delivered to them
the second key to the Electrical Show which I had promised a few days ago.
The second key is:

Heat (and light) is produced by offering resistance to the flow of the electric
current. The first key is the electro-magnet. These two unlock all the
mysteries of the show.
The president closed the formal exercises with the facetious remark that I
had warned them before the lecture that they must work, so now each
would be expected to take a turn at the cranks of the pump and dynamo.

VIII

APPLICATIONS OF ELECTRIC HEATING
he programme committee decided that each member of the Science

T Club should busy himself looking for applications of electric heating
and should consult me freely about the matter. My telephone was kept
busy, my laboratory was in great demand, and we were all getting a good
deal more education than the school was giving us credit for.
The boys generally came to me in pairs, and each pair having worked up
some illustration of heat produced by electricity reported it to the club.
These were spread by the secretary in due form upon the minutes of the
club and constituted "The Proceedings of the Science Club."
1. The Electric Sad Iron (Fig. 69).—
Removing three screws the iron comes
apart, revealing a lot of No. 24 German
silver wire wound upon a sheet of mica.
This is put between other sheets of mica
(Fig. 70) and tucked away within the body
of the iron. German silver offers about
twice the resistance of iron when it is cold,
but, at the temperature of the sad iron
when in use, there is not much difference
Fig. 69 between the resistance of the two metals.
German silver wire, however, does not rust
as iron wire would, and hence it is chosen.
German silver is an alloy of copper, zinc, and nickel.
We put the 112-volt current upon this wire of the iron, and according to the
ammeter it passed 4 amperes. Its resistance must therefore have been 28
ohms.
(112 volts)/(28 ohms) = 4 amperes

Electricity costs us about 10 cents per
kilowatt hour. That is 10 cents for 1000
watts for an hour, or 1 cent for a hundred
watts for an hour, or, on a 100-volt current,
1 cent for an ampere for an hour. It,
therefore, costs about 4 cents or, more
Fig. 70 accurately, 4½ cents an hour to heat this
iron.
Persons sometimes carry electric irons with them, when they travel, to iron
pocket handkerchiefs and other small articles while stopping at a hotel.
Before connecting an iron in a chandelier one must know the voltage used
in the building. If the voltage in use in the building is not the same as that
stamped upon the iron, it is not safe to connect it. Not knowing this, many
persons have had the embarrassment of "blowing a fuse" and extinguishing
their own lights, and perhaps those of others in the same building, and very
likely also ruining the iron.
Suppose we take for example this iron stamped 110 V; 400 Watts. (A slight
variation of 5 or 10 volts will not injure an iron.) The wire in this iron we
found to offer about 28 ohms resistance when hot, and it lets pass 4
amperes. This is about all the current which it is able to carry without
melting. Now suppose a 220-volt current is used in the building where it is
proposed to connect the iron. This would force through the wire enough
current to melt it. The wire was seen to be at a very dull-red heat when
examined in a dark room. Its temperature was about nine hundred degrees.
At this temperature its resistance is about three times what it is when cold.
We estimated by measurements that the iron contained about twenty-five
feet of the wire. The boys then took twenty-five feet of No. 24 German
silver wire and stretched it between two nails driven up in the laboratory
(Fig. 71, a b). The dynamo current was then sent through this. The end, c,
of the wire from the dynamo was provided with a metal clip which could be
slid along on the German silver wire. Sliding this to the left, and thus
shortening the distance on the German silver wire through which the current
must pass, increased the amount of current and heated the wire hotter. The
resistance decreases as the wire is shortened.

Fig. 71

The boys wound this wire upon a piece of
asbestos board (Fig. 72), about nine inches
square and one eighth of an inch thick, taking
care to keep the successive turns half an inch
apart. Asbestos paper was wrapped around this.
The two ends of the wire were left free for
connections. This they called a "hot plate."
2. Electric Hot
Plate (Fig. 73).
—This when
Fig. 72 opened was
found to have
wire coiled up inside in the same manner
as the sad iron. Indeed the sad iron
supported bottom side up makes a Fig. 73
perfectly good hot plate. The particular hot
plate which we examined had a three-point
switch which gave three different heats for the plate. (See Fig. 74.) When
the switch S is upon the first point the current goes through 112 ohms of
resistance and 1 ampere passes:
(112 volts)/(112 ohms) = 1 ampere
This warms the plate slightly—enough to keep food warm which has been
already cooked. This costs about one cent an hour.
When the switch is placed upon the second point the current goes through
56 ohms of resistance and 2 amperes pass.

(112 volts)/(56 ohms) = 2 amperes.
This makes the plate warmer and is
adapted to certain cooking processes. It
costs about two cents an hour.
When the switch is placed upon the third
point the current goes through 28 ohms of
resistance and 4 amperes pass.
Fig. 74 (112 volts)/(28 ohms) = 4 amperes.
We placed upon this hot plate a basin
containing 1 pint of water (equals 1 pound) and heated it from the
temperature of the room (68 degrees) to boiling (212 degrees) in 7 minutes
and then put an egg in and boiled it 3 minutes. Using 4 amperes for 10
minutes cost two thirds of a cent. If it takes 7 minutes to boil a pint of water
it would require 1 hour to boil a gallon upon this hot plate using 4 amperes,
or 448 watts. That is, it costs us about 4.5 cents a gallon to boil water by
electricity. The cost is usually put at three and a half cents per gallon, but
much depends upon conditions.
3. Traveller's Cooker (Fig. 75).—This
consists of a hot plate with a covered basin
permanently attached to it.
4. Electric Coffee Percolator (Fig. 76)
consists of a hot plate with a coffee
percolator to sit upon it. The coffee
percolator might sit upon any other hot
plate or this hot plate might serve any
Fig. 75 other purpose, but people do not seem to
think of that.
5. Electric Chafing-Dish (Fig. 77) consists merely of an electric hot plate
with a chafing-dish attached. The electric coffee percolators and chafing
dishes require from 300 to 600 watts according to size. If used on the 110-
volt current they take about 3 to 6 amperes, and if adapted to the 220-volt
current they take from 1½ to 3 amperes, but cost the same to operate in
either case. They have connected with them flexible cords and plugs to
screw into the lamp sockets.

6.
Electric
Broilers
are
merely
hot
plates,
generally
corrugate
d to
Fig. 77
conduct
off the
melted fat. One that we examined had a
switch for three heats: low, requiring 360
watts—costs 3.6 cents per hour; medium, Fig. 76
requiring 600 watts—cost 6 cents per
hour; high, requiring 1280 watts—cost 12.8 cents per hour.
7. Electric Oven.—This one has double walls to retain the heat and has two
large hot plates, one on the bottom and one on the top. It is large enough to
hold four loaves of bread. It required 1520 watts for 40 minutes to heat it to
the baking temperature and one hour to bake the bread. Hence the cost of
the electricity is about 25 cents, about what the bread would cost in the
market.
8. Electric Incubator.—This is simply a well-ventilated oven warmed by an
electric hot plate and automatically controlled so that it keeps a constant
temperature of 103 degrees. Under these conditions chickens hatch from
hens' eggs in three weeks. An incubator for 5 dozen eggs was found to take
25 cents' worth of electricity for the whole process of incubation.
9. Electric Toaster.—The wire coiled up in sad irons and hot plates becomes
hot enough to scorch cloth and paper, and even set fire to them if they come
in direct contact. We proved this by opening the iron and touching paper to
the wire while it was carrying the current. We also lighted a cigar by
touching it to the wire. Electric toasters have the hot German silver wire
simply covered by a screen.

10. Electric Cigar Lighters (Fig. 78).—The one we
examined hung by a flexible cord from the chandelier.
It had a small disk on the side which contained a lot of
fine wire covered by perforated mica. The wire
became red hot when the push button in the handle
was pressed. It took half an ampere of 110-volt
current, and operated only while the button was
pushed. As near as we could calculate it cost .0003 of
a cent to light a cigar.

Fig. 78

Fig. 79

11. Electric Curling Iron (Fig. 79).—One who has flat hair needs no curling
iron, but those who have round hair may curl it temporarily, if they will
unscrew an electric light bulb and screw into its socket the plug of an
electric curling iron. The flexible cord contains two wires insulated from
each other. One of these wires is attached to the outer shell of the plug, the
other wire is attached to the central button of the plug. These make
connections with the two separate dynamo wires in the socket. The current
comes down one of the wires in the flexible cord, passes through a coil of

fine German silver wire inside of the curling iron, and
returns by the other wire in the flexible cord. The small wire
in the curling iron offers 220 ohms of resistance when hot
and passes half an ampere of the 110-volt current.
(110 volts)/(220 ohms) = .5 ampere.
12. Electric Soldering Irons (Fig. 80).—Or coppers, as they
should be called, are ideal implements for soldering. They
remain continually at the proper temperature and are free
from corrosion. They require from 55 to 220 watts. On the
110-volt current they take from one half to two amperes.

Fig. 80

Fig. 81

13. Electric Heating Pad (Fig. 81).—This consists of resistance wire inside
of a pad of soft material. It maintains a temperature of 180 degrees, and is
an excellent substitute for a hot water bag. It contains about two hundred
and twenty ohms of resistance and requires the same current as a 16-candle-
power lamp.
14. Electric Fuses (Fig. 82).—Fuses are
made of short pieces of wire or thin sheet
metal. The metal is an alloy of lead and tin
which melts at a low temperature. They
derive their name from the fact that they
readily fuse or melt. A building is wired in
various separate circuits. The size of the
copper wires used in each circuit is
determined by the amount of current
which the circuit is expected to carry. Each
circuit is protected by one or more fuses.
These melt and cut off the current
whenever too much passes for the copper
conductor to carry without getting hot. The
fuse wire melts at about six hundred

Fig. 82 degrees, while the copper will not melt
until it reaches nearly two thousand
degrees. This temperature is sufficient to set fire to wood, paper, and cloth.
When any fuse melts, the current is cut off from all chandeliers, etc., in the
particular circuit controlled by the fuse. This produces consternation among
people who do not understand the function of a fuse. They become panic-
stricken and begin to trample their neighbours to death in the theatre or on
the electric train when they hear that a fuse is "blown" (which is the
electrician's way of saying that it has melted). Everyone should know that a
fuse is a safety device. It is always enclosed in a box lined with sheet iron
or asbestos, so that it is impossible for the flash, which occurs when the
circuit is broken, to set fire to anything.

Fig. 83

15. Electric Gas Lighter (Fig. 83).—These usually have two or three small,
dry battery cells in the handle. By pushing a button in the handle connection
is made between this battery and a short piece of resistance wire in the tip.
This wire gets red hot and lights the gas. It is a surprise to many that we can
light illuminating gas without bringing a flame to it, and it is equally
surprising that some flames, or at least sparks, may not be able to light the
gas. The fact is that it is wholly a matter of temperature and kind of gas.
Iron heated to dull red will not light the illuminating gas now being
furnished in New York City, while iron at a bright red heat will do so. Iron
may be hot enough to light illuminating gas but too cool to light gasolene
vapour, which requires a dazzling white heat. Iron which is just under the
temperature at which it gives any light may set fire to wood and paper. After

it has cooled a good deal below that, it will set fire to sulphur, and when it
has cooled so that one may hold it in the hand, it is still hot enough to set
fire to phosphorus. The glowing end of a lighted cigar, the spark made by
striking flint, or the spark from a spark coil with a feeble battery, all fail to
set fire to gasolene vapour, simply because they are not hot enough.
Fresh battery cells must occasionally be put in the handle of the electric gas
lighter.
Four facts regarding the resistance of wires it is well to remember:
1. The longer the wire the more resistance it offers to the electric current.
2. The smaller the diameter of the wire the more resistance it offers.
3. Some materials offer more resistance than others, for example, iron about
six times as much as copper and German silver about twelve times as much
as copper.
4. The common metals offer more resistance when hot than when cold,
about double the resistance when heated to five hundred degrees. It is the
reverse with carbon, which offers more resistance when cold than when hot.
The carbon filament lamp offers about double the resistance when cold as
when lighted to full brilliancy.
16. Electric Flasher (Fig. 84).—For
automatically flashing electric lights. The
one which we examined was constructed
according to the plan shown in Fig. 85.
The lighting circuit is brought to the Fig. 84
binding posts b and c. A small insulated
wire of high resistance connects b and c, being wound around the metal bar
a b. The resistance of this wire, when added to that of lamps, permits not
more than one fifth of an ampere to pass, and this warms the wire slightly.
The bar a b is composed of two strips of metal, brass above and iron below.
Heat expands brass more than iron. The result is that when the current is
turned on, the bar begins to curve downward until presently it touches the
metal base of c. Then the full current required to light the lamps which are
in circuit passes. While the circuit is closed through the large metal strips
not enough passes through the fine wire to warm it. On cooling, a b curves

upward and breaks the connection with c, and now the current begins again
to warm up the small wire.
The flasher that we examined was adapted
to operate: one 32-candle-power lamp; or
two 16-candle-power lamps; or four 8-
candle-power lamps, on a one ampere
circuit of 110-volt pressure.
Fig. 85 Let us see what would happen if it were
connected either with a current of higher
voltage or a circuit of more lamps. Suppose we have a 32-candle-power
carbon filament lamp in circuit. This requires one ampere to light it. Its
resistance when hot is 110 ohms.
(110 volts)/(110 ohms) = 1 ampere.
When cold its resistance is about double or 220 ohms. The German silver
wire of the electric flasher offers 330 ohms of resistance, and together they
make 550 ohms. Thus the current is cut down to .2 ampere.
(110 volts)/(330 + 220 ohms) = .2 ampere
Suppose now we should undertake to use the same flasher and the same
lamp on a 220-volt current. This might push more current through than the
small wire could carry. It might melt, or its insulation might burn off before
a made contact with b; if not the lamp would certainly burn out after the
contact. If we undertook to operate with this flasher several 32-candle-
power lamps instead of one upon the 110-volt circuit, the result would be
the same, for in that case the resistance would be reduced and, therefore, a
greater current would pass than the wire could carry without undue heating.

Fig. 86

The boys were at first troubled to see how increasing the number of lamps
in a circuit would decrease the resistance in that circuit. Fig. 86 was drawn
to explain the matter. The lamps l, l, l, etc., are connected in parallel. Each
lamp makes an independent connection from one feed wire to the other. The
flasher a acts as a switch to close the circuit for the whole.
Now if we think of these wires as pipes to conduct water we would say that
water flows from D to E through ten pipes more readily than through one. It
would meet with only one tenth as much resistance. The result would be the
same, if we should substitute for the ten pipes one pipe ten times as large in
cross section. So it is with wires which are conducting electricity. Introduce
two in parallel, and you allow twice as much current to pass by reducing the
resistance to one half. Ten parallel conductors reduce the resistance to one
tenth and allow ten times as much current to pass.

Fig. 87

It is to be noticed that this flasher is an automatic switch which is opened or
closed according to temperature. Remove the fine wire from a and we have
precisely the device which regulated the temperature in our electric
incubator. Suppose the "thermostat" (as it is called in that case) is placed
within the egg chamber which is to be kept at 103 degrees. A screw in the
metal strip c underneath the end of a may be set so that it will normally
touch a. Suppose now the brass strip is underneath the strip of iron in a. As

the hot plate warms up the egg chamber, the brass will expand more than
the iron, and the bar will curve upward and break the connection with c. As
soon as the current stops the temperature of the chamber begins to fall, and
the bar curves downward again until connection is made. This device is
capable of adjustment so as to keep the temperature constantly at 103
degrees or any other desired degree. The device is in use for scores of
different purposes, including the regulation of temperature in school rooms.
17. Electric Car Heaters.—Ten or fifteen years ago there were no heated
street cars in New York City. Now they are all heated by electricity and
their maximum and minimum temperatures are regulated by law. The
resistance wire may be seen in coils underneath the car seats. Electric street
cars usually operate on a 500 or 600-volt current. The amount of current
used for heating varies from 2 to 12 amperes. Perhaps 3 amperes may be
taken as an average.
500 V × 3 a = 1500 w = 1½ kilowatts.
It costs the large electric railway companies about 1.5 cents per kilowatt
hour to generate their supply of current. Eighteen hours is considered a car
day.
1½ kilowatts × 18 hours = 27 kilowatt hours.
27 kilowatt hours at 1.5 cents = 40 cents per car day.
18. Heating Apartments by Electricity.—For heating apartments by
electricity the same sort of apparatus is used as that already described for
heating cars. A family of four adults, living in an eight-room apartment with
at least 120 cubic feet of fresh air admitted per minute, will use on an
average ten amperes of the 110-volt current. The cost will be about two
dollars and fifty cents per day or seventy-five dollars per month. Although
this is as much as the entire rental of a perfectly comfortable apartment, the
novelty and the convenience attract tenants and the extra cost of rent does
not deter them.
19. Electric Bedroom Heater.—One of the boys constructed a heater for his
own room as follows: He procured a box eight inches deep by eighteen
inches square on the bottom. This he lined with asbestos paper. He then
stood it upon its side and arranged four incandescent light sockets as shown
in Fig. 88. These were connected by a flexible cord to a plug which he

could insert in place of a lamp in the
chandelier. He placed this heater on the
floor underneath the window and usually
had 16-candle-power lamps in the sockets.
He claimed that it was a jolly foot warmer
and kept the room comfortable without
other heat. He turned on from one to four
lamps according to his need and replaced
the 16-candle-power lamps by 32-candle-
Fig. 88
power lamps when the weather was
extremely cold. I remarked that he must
have light along with heat by this arrangement, and I should think that
might be objectionable when he desired to sleep at night. He said that he
always turned it off, and opened the window at night, always preferring a
cold room to sleep in.

Fig. 89

20. Cooking with Incandescent Lamps.—This piece of apparatus was
devised by the boys and used in my laboratory. A sheet iron basin a, was
inverted over four 16-candle-power incandescent lamps, shown in elevation
by Fig. 89, and shown in plan by Fig. 90. The sides of the basin were cut so
as to admit the glass globes of the lamps, but the sockets and keys were
outside, so that it was convenient to turn on and off the lamps separately,
thus using one half to two amperes of current, as desired. This rested upon
another basin, b. Basin b was covered with asbestos for the lamps to lie on

and the whole was attached to a board base, c. A flexible cord and plug
allowed us to attach this to the chandelier. A pint of water was boiled upon
this stove in fifteen minutes, and refreshments have been served hot from it
repeatedly.

Fig. 90

21. Electric Fireless Cooker.—There are five indictments against ordinary
cooking processes.
1. They heat the house in summer.
2. They convert what would be pleasant flavours in the food into noxious
odours about the house.
3. They cannot be controlled with regard to time and temperature as
scientific experiments should be.
4. They confine the cook too closely and are not sufficiently automatic.
5. They are wasteful of fuel.

It would seem that electricity might enable us to cure most of these evils. To
be sure the production of heat by electricity is wasteful of fuel, and it seems
doubtful how the account will balance regarding the fifth item. But the
remaining four items furnish a very hopeful field for research. I use the last
word advisedly, and think it is just as applicable to high school boys as to
university students. After experimenting awhile the boys and I concluded to
give a dinner party in the laboratory and invite a few friends to test the
results of our cooking.
We procured a cylinder of magnesia such as is used for covering large
steam-pipes. This was inverted over our electric stove which was illustrated
in Fig. 89. The magnesia was cut at the bottom, so as to give access to the
key sockets of the lamps, (Fig. 91). First upon the electric stove was placed
a covered dish containing a roast of lamb. Above this was another dish
containing a vegetable, and upon the top of that was a pudding. A flat piece
of magnesia was used as a cover to the whole. Through a hole in this was
suspended a thermometer.

Fig. 91

This "fireless cooker" was sitting in the centre of the dinner table when the
guests gathered around it. We had these problems for investigation:
1. Will this cooker heat the house in summer?
All testified that they did not know that there was any heat about it until
they laid their hands upon it, and then they found it only very slightly
warm.

2. Is there any smell of cooking here? The process has been carried on from
start to finish right on this table.
All agreed that no smell could be detected.
I then turned off the electric current which had been running until now and
served the meat and vegetable, leaving the pudding inside to be kept warm
by the hot walls of the cooker.
3. Regarding the control of the process: we were using 32-candle-power
lamps, which gave us a variable current, from 0 to 4 amperes, and a watch
and a thermometer. We had control, but as yet lacked knowledge of how it
should be used. In the present case we had arbitrarily decided to begin with
temperature of 400 degrees, continue it for 20 minutes, then turn off all the
electric current, and let the temperature fall gradually. This had been done at
our convenience in the morning before school. At a quarter before twelve
we had found the temperature at 200 degrees, and turned on all the current,
and now, at five minutes past twelve o'clock, all testified that the lamb was
particularly good—neither too well done nor undercooked, and that its
flavour was better than usual.
As for economy of fuel, we find at least that we get better results from
incandescent lamps than from hot plates used in the same apparatus, and the
electric equipment enables us to put the heat exactly where it is needed and
nowhere else.
22. Incandescent Lamp.—We feel quite justified in putting the incandescent
lamp under the heading, Applications of Electric Heating, since the electric
lamps in general use convert 96 per cent. of the electric energy into heat and
only 4 per cent. into light.
They were originally made by introducing a short piece of fine wire into the
circuit, choosing the kind of wire, its diameter, and its length so as to make
the proper relation between resistance and voltage, in order that enough
current might pass to make it white hot, but not quite melt it. Platinum wire
was first chosen because it would stand the highest heat without melting
and without rusting.
We will pass our 112-volt current through 9 feet of the No. 24 iron wire.
The wire is heated to bright red, but does not melt as it did when we used 8
feet in a former experiment. The increased length has added resistance, and,

as you see by the ammeter, cut the current down from 8 to 7.5 amperes. I
will now darken the room and you find that it is giving light enough to read
by. But you notice that the light is growing dimmer, its colour is growing
redder, and the ammeter indicates that less current is passing. I will cut off
the current and let you examine the wire and you notice that a crust has
formed upon it. This is due to the oxygen of the air which unites with the
iron, forming iron rust. Iron rust does not conduct electricity. We have
converted No. 24 iron wire into a wire of smaller diameter with a sheath of
iron rust around it. We might prevent the rusting by putting the wire in a
glass globe and exhausting the air from it.
I have here a piece of No. 24 platinum wire which has about the same
resistance as iron wire when cold, but you notice that I may use a very
much shorter length than I did of the iron wire because it will endure a very
much higher heat without melting. Reducing the length would reduce the
resistance, but reducing the resistance would allow more current to pass. If
more current should pass it would make the wire hotter, and raising the
temperature would increase the resistance, which would cut down the
current, etc. By sliding the clip c (Fig. 92), along, I finally reach a point
where conditions balance so that I get a very brilliant light, dangerously
near the fusing point of the platinum which is three thousand degrees above
the boiling point of water.
In 1879 Mr. Thomas A. Edison literally searched the whole world for
something better than platinum for the filament of an incandescent lamp.
He finally decided upon charred threads of a bamboo which he found in
Japan. No research was ever more timely than this. Whereas there was
practically no electric lighting before 1880, soon after that there began a
phenomenal demand for carbon filament lamps. In 1890, 800,000 of these
lamps were manufactured in the United States. In 1900 the number had
risen to 25,000,000. In 1909 central stations were supplying electric current
to 41,807,944 incandescent electric lights. By far the greatest number are
still made with carbon filaments.

Fig. 92

We examined an ordinary 110-volt 16-candle-power
carbon filament lamp, (Fig. 93). As near as we could
estimate, its filament measured about eight inches in
length. We broke open the bulb of this lamp by laying
it upon the table and tapping it with a board. The bulb
broke with rather a loud noise and the brittle carbon
filament broke into many pieces. We found one of
these pieces and measured its diameter with a wire
gauge, (Fig. 94). It was the same size as No. 33 wire,
which we also found by the wire gauge was the size of
No. 90 sewing cotton. The diameter of No. 33 wire
was given upon the wire gauge as .007 inch. When
lighted, the filament of this lamp had looked to be
Fig. 93 about the size of No. 18 wire, which has a diameter of
.04. That is, the filament when lighted looked six times
as thick as it really was. Those who use sewing cotton learn quickly to
know the size of the thread by its number. So those who have much to do
with wire easily learn the system of designating sizes by numbers. Here are
some selected figures easy to remember. A trolley wire is about one third of
an inch in diameter. It is designated as No. 0. Notice in the following table
that as the numbers rise by six the diameters are divided by two. Notice also
that as the diameters diminish by two the resistance increases by four.
TABLE OF RESISTANCE OF COPPER WIRES
Nos. Diameter Resistance
0 .32 inch 10560 feet to the ohm
6 .16 " 2640 " " " "
12 .08 " 660 " " " "
18 .04 " 165 " " " "

24 .02 " 40 " " " " Fig. 94
30 .01 " 10 " " " "
36 .005 " 2.5 " " " "
42 .003 " 1 " " " "

10,560 feet equal two miles.
Number 36 is the wire used upon the spools of telegraph receivers. They
offer 75 ohms of resistance and therefore contain 30 feet of wire (30 × 2.5 =
75). These resistances are for ordinary school room temperatures.
Since iron has six times, and German silver twelve times the resistance of
copper, divide the figures of the third column by six, and the table will
answer for iron wire, or divide those figures by twelve and the table may be
used for German silver wire, thus:
Number Feet to the Ohm
Nos. Diameter Copper Iron German Silver
0 .32 inch 10560 1760 880
6 .16 " 2640 440 220
12 .08 " 660 110 55
18 .04 " 165 27 14
24 .02 " 40 6 32 inch
30 .01 " 10 1.5 8 "
36 .005 " 2.5 .45 2 "
42 .003 " 1 2 inch 1 "

These figures are not exact, but useful.
We procured a string of eight small lamps (Fig. 95), such as are used in
lighting Christmas trees. Each was marked 14 volt, 2-candle-power. The
carbon filament of each was about one inch long and apparently the same
diameter as that of the 16-candle-power lamp. When the 110-volt current
was sent through the group of eight connected in series they seemed to give
about the same light as the single 16-candle-power lamp. It is as though the
filament of the 16-candle-power lamp had been cut into eight pieces, and
distributed through eight small lamps. We introduced an ammeter into the
circuit and found that half an ampere of electricity passed through the single
16-candle-power lamp—and half an ampere likewise passed through the
group of eight 2-candle-power lamps.
The 110-volt current can push an ampere of electricity through eight inches
of carbon thread seven thousandths of an inch in diameter, and when this

happens the filament gets hot enough to
give out as much light as sixteen standard
candles. In the place of the 16-candle-
power lamp, we put a 32-candle-power
110-volt lamp. The ammeter indicated one
ampere. The carbon filament was larger
(No. 30, diameter = .01 inch), so as to
allow more current to pass. An 8-candle-
power 110-volt lamp was substituted; one
quarter of an ampere passed. A 4-candle-
power 110-volt lamp was used; one eighth Fig. 95
of an ampere passed. A 100-candle-power
110-volt lamp was substituted; three amperes of current passed through it.
In all these cases the lamps which passed the larger current had the larger
filaments. A little practice would enable one to distinguish between these
lamps without labels by examining their filaments. Among these 110-volt
lamps, it is to be noted that the amount of light which they give is
proportional to the amount of current which they pass. And it is convenient
to remember that one ampere of electricity for one hour costs about one
cent.
We introduced into the socket a "Hylo" lamp (Fig. 96). The filament, A,
took half an ampere of electricity, gave 16-candle-power of light, and cost
half a cent an hour. When the lamp was turned in its socket the current was
switched off of the filament A, and on to the filament a. This took .03 of an
ampere, gave one candle-power of light, and cost .03 of a cent an hour, or at
the rate of about $3.00 a year, burning continuously day and night.
The uses of such a lamp are apparent in rooms which have no daylight.
However, a wall switch at the entrance of such a room, making it easy to
throw on and off the light entirely, seems to be a more satisfactory
arrangement. One of the boys connected a wattmeter in the circuit with a
hylo lamp and found that the small filament did not pass current enough to
move the armature of the wattmeter. Hence that may be burned alone
without affecting the consumer's bills.
We took a 16-candle-power 220-volt lamp, and lighted it by a 220-volt
current. The meter showed that it allowed only one quarter of an ampere to
pass. The filament was very much smaller than that in the 110-volt, 16-

candle-power lamp. The pressure was
twice as great as before, but the resistance
was four times as great, and hence only
half as much current passed. We find that it
costs just as much to generate one quarter
of an ampere at 220-volt pressure as it
does to generate half an ampere at 110-volt
pressure.
We must, of course, pay for electricity
according to the cost of producing it. To
produce .5 ampere at 110-volt pressure
costs the same as one ampere at 55-volt
pressure, or .25 amperes at 220 volts. It
will be noticed that the products of the two
factors in each case are the same. The
product of an ampere multiplied by a volt
is a watt. In each of the above three cases
the amount of electrical energy is 55 watts. Fig. 96
This will produce a definite quantity of
light—about 16 candle-power when the carbon filament is used, and this
quantity does not vary as either volts or amperes, but as the product of
these, namely, watts.
Each of these lamps is called a 55-watt lamp, and, since they each give 16
candle-power of light, a carbon filament lamp gives one candle-power of
light for three and a half watts of electricity. Electricity for lighting
purposes usually costs 10 cents per kilowatt hour, that is, 10 cents for 1000
watts for one hour, or one cent for 100 watts for one hour. Hence a 55-watt
lamp costs a trifle more than half a cent for one hour, or exactly .55 cents,
and a 32-candle-power lamp costs 1.1 cents per hour.
We introduced into the socket a 48-candle-power 110-volt tungsten lamp
(Fig. 97), and turned on the 110-volt current. The ammeter showed 55
ampere. Hence the lamp is a 60-watt lamp, and requires one and a quarter
watts per candle-power. That is, the metal tungsten is nearly three times as
efficient as carbon for producing light from electricity.

With pincers we broke off the tip of a 32-
candle-power carbon filament lamp,
making a small hole in the large end of the
bulb. The air rushed in. We then put the
lamp in the socket and turned on the
current. The carbon filament glowed as
usual, and slowly burned up, growing
smaller as it did so. The ammeter which
was in circuit showed that the current,
which was one ampere at the beginning,
grew steadily less as the filament grew
smaller, until finally when it was about one
quarter of an ampere, the circuit was
broken by the filament burning in two. We
removed the lamp from the socket and
with a dropper tube introduced a little lime
water, and shook it to absorb any gas
which might have been formed in there. It
became milky white, as it always does
when introduced where carbon has been
burned. This would be a sufficient proof Fig. 97
that the filament was made of carbon, if
we did not already know it. The air is
exhausted from these bulbs to prevent the carbon filament from burning up.
The carbon filament lamps were, as has
been said, the invention of Mr. Thomas A.
Edison in 1879. Such a statement must,
however, be qualified by the assertion that
this, like nearly all invention, was but the
consummation of a long line of researches
made by many men for many years. The
early filaments were made of bamboo
thread, charred, but now they are drawn
like spider's web out of a sticky liquid and
carbonized at a high temperature. They are
attached in the lamp to short pieces of Fig. 98
platinum wire which are sealed through

the glass walls of the bulb. One wire connects with the brass collar of the
bulb, and the other with the central piece of brass at the base of the bulb.
We dissected a socket and found that when the lamp is placed in the socket,
the collar of the lamp is screwed into the collar of the socket, and the base
of the lamp comes in contact with a brass spring in the bottom of the socket
(Fig. 98). The spring is connected with one copper wire bringing electricity
from the dynamo. The collar is connected with the other wire from the
dynamo. This connection is made and broken by turning the key of the
socket. The wires are made of copper since copper is a particularly good
conductor of electricity. No electricity can flow unless this circuit is
complete. Socket keys and wall switches make or close gaps in this circuit.
No copper wires for carrying electric-lighting current are smaller than No.
12, which has a diameter of .08 or about one twelfth of an inch. The
intention is to have as little resistance to the current as possible, except in
the filament of the lamp itself. There resistance is purposely introduced in
order to convert electricity into light, light without heat if that were
possible, but since that has not yet been found possible, heat for the sake of
the accompanying light. Unhappily only 4 per cent. of the electrical energy
goes into light and 96 per cent. goes into useless, or even harmful, heat. The
tungsten lamps, which are now coming into use, are nearly three times as
efficient in the production of light as are the carbon filament lamps. The
dynamo exerts its entire pressure upon the lamp and furnishes current as
follows:
A dynamo of 110-volt pressure gives:
1 ampere = 110 watts, through a 32-candle-power lamp, cost one cent an
hour, or
.5 ampere = 55 watts, through a 16-candle-power lamp, cost half a cent an
hour, or
.25 ampere = 27½ watts, through an 8-candle-power lamp, cost a quarter of
a cent an hour.
A dynamo of 220-volt pressure gives:
.5 ampere = 110 watts, through a 32-candle-power lamp, cost one cent an
hour, or

.25 ampere = 55 watts, through a 16-candle-power lamp, cost half a cent an
hour, or
.125 ampere = 27½ watts, through an 8-candle-power lamp, cost a quarter
of a cent an hour.
The carbon filament lamps, barring accidents, have a natural life varying
from 600 to 1000 hours of actual incandescence. At the end of that period
the filament has become so thin that it will fall apart by ordinary usage. It is
never profitable, however, to use them for their whole lifetime. The lamp
gradually volatilizes carbon and deposits it upon the inner walls of the bulb,
producing a smoky appearance and shutting off light. As the filament grows
thinner by this process, it offers greater resistance to the current, and as the
amount of current grows less the proportion of light to current grows
rapidly less, so that at last instead of paying for 3.5 watts of electricity per
candle-power of light one must pay for perhaps seven or eight watts per
candle-power. We pay fifteen cents apiece for 16-candle-power lamps, and
it is economy to renew them about twice a year, if they are burned, say three
hours a day, or a little over five hundred hours. It is interesting to note that
when a direct current is used the evaporation from the carbon filament
always takes place at the negative end alone, that is, the end from which the
current is leaving the lamp. If an alternating current is used the evaporation
goes on from all parts of the filament alike. This is a case of evaporation
from the solid state. Carbon does not boil below 6,000 degrees, and the
filament reaches about 2,450 degrees.
Tantalum, tungsten, and osmium lamps have metal filaments. These metals
are better conductors than carbon but unlike carbon their resistance
increases as their temperature rises, and their special virtue is that they are
capable of enduring an extremely high temperature without melting. The
wire used in some of these filaments is as small as .002 of an inch, or No.
44. In order to furnish sufficient resistance to prevent the 110-volt current
from melting, they often have a length exceeding two feet. This is laced
back and forth within the small bulb. At the temperature of bright
incandescence their resistance may be increased as much as fivefold and
sometimes becomes about ten ohms to the inch. Like all metals they are
more brittle when cold than hot. Hence when cleaning such lamps it is
advisable to turn on the current to avoid breaking the filament by jarring.

Filaments which are too fragile to endure the jar of ordinary railway travel,
when cold, have gone through railway wrecks safely when lighted.
It is a general rule that good conductors of electricity grow more resistant as
the temperature rises while non-conductors resist less as the temperature
rises. Hence the insulating material which is used to cover copper wires
fails to protect if highly heated.
If a 110-volt lamp is put into a 220-volt circuit, one might expect that the
lamp would burn out without doing further damage to the circuit, but this is
not the case. As the filament approaches its melting point, 6000 degrees, it
becomes so good a conductor that it carries current enough to melt a fifteen
ampere fuse. It is, therefore, the fuse that protects the circuit and not the
burning out of the lamp. The bulb containing the highly heated carbon
vapour would conduct the current as an arc lamp does.
23. Arc Lamp.—We fastened two electric
light carbons to the ends of copper wires
connected for the 110-volt current. A
rheostat, R (Fig. 99), in circuit, was set at
6.5 ohms. One lower carbon was fastened
into a clamp, and the other was touched to
it, and then drawn away about three-
eighths of an inch. A very brilliant light
was produced. Probably about 1800
candle-power. The ammeter A showed 10
amperes, and the volt meter V showed 45
Fig. 99
volts. 45 volts × 10 amperes = 450 watts,
1800 candle-power, 25 watts per candle-
power.
The arc light is the cheapest of all lights but is too dazzlingly bright for
household purposes. It is used for outdoor lighting chiefly, and particularly
for large search-lights. The temperature is over 6000 degrees, which boils
the carbon and fills the gap between the two pencils with a stream of carbon
vapour. This conducts the current like the filament in an incandescent lamp.
The air gap between the carbon pencils would have a resistance of many
thousand ohms if it were not for the presence of the carbon vapour. The hot
carbon vapour reduces the resistance of this space to 4.5 ohms.

(45 volts)/(4.5 ohms) = 10 amperes.
or
(110 volts)/(6.5 + 4.5 ohms) = 10 amperes.
The carbon pencils account for part of this resistance—not more than a
third of an ohm however.
It is evident that arc lamps in use must have an automatic mechanism which
shall permit the carbons to touch whenever the current is not passing, but
which shall draw them apart to the proper distance after the carbon vapour
has been formed, or, as we say, after the arc has been established. This
mechanism is nothing else than electro-magnets which are operated by the
lighting circuit itself. It may require thoughtful examination to recognize
these as electro-magnets, in every case, but that is what they are. Sometimes
they are coils of wire, which do not have iron cores and armatures separate
to be sure—but nevertheless they have both of these united in one movable
rod, and they produce magnetic fields.
Suppose I pass an electric current around this coil A (Fig. 100). The region
about the coil becomes a magnetic field with its north pole situated at a
point in space, say N. The influence of this field causes the iron rod to
become a magnet with its south pole uppermost, and if the current is strong
enough, and the field which it produces is strong enough, it will lift the iron
rod up into the coil. By varying the strength of the current you see I may
make this rod dance up and down in space touching nothing—a veritable
ghost dance.
It may be pettifogging to say that the upper
portion of this iron rod is the core of the
magnetic field, and its lower portion is the
armature. Yet this is right, and pettifogging
may be right when it is the only way to
bring out the fact.
Our great study now is to produce light
without heat, or at least to come as near to
it as the firefly does. The firefly gives 98
per cent. light and two per cent. heat. The Fig. 100
arc lamp gives 12 per cent. light and 88

per cent. heat. The carbon filament gives 4 per cent. light and 96 per cent.
heat. When we have made considerable progress in that direction we shall
take electric lamps out of the chapter on electric heating and form a new
chapter on electric lighting.
One might expect that a rod made of carbon would quickly burn up,
particularly when raised to the exceeding high temperature of the electric
arc. While it is true that carbon in the form of charcoal burns so readily that
it is used instead of kindlings for lighting a fire, carbon in the form of
graphite in our so-called "lead" pencils and carbon as it is prepared for
electric light pencils burns only very slowly even at exceedingly high
temperatures. The carbon rods used in arc lamps endure a temperature of
over 6000 degrees, without losing more than one inch an hour, and half of
that is simply volatilized—not burned.
One of the most interesting improvements ever made in the arc light is that
of enclosing the arc in an inner glass globe. This globe is closed airtight
below with a small opening above. When the arc is formed the oxygen of
the air in the inner globe is soon consumed and then combustion is no
longer possible. We illustrated this by an experiment. An ordinary cork was
chosen to fit the large end of an argand lamp chimney and through a hole in
this was passed one of the carbon rods (Fig. 101). A metal clamp made
connections between this carbon and the negative wire from the dynamo.
The other carbon, attached by a clamp to the positive wire, was thrust down
into the upper end of the chimney until it touched the negative carbon, and
then drawn upward a short distance, drawing an arc, as we say. This soon
makes an atmosphere within the chimney where combustion cannot go on
for want of oxygen. The arc, however, continues to glow as in the open air,
and the carbons may be drawn further apart than in the open air without
breaking the arc, hence more of the external resistance may be cut out and a
higher voltage put upon the lamp.
Carbons which burn out in a single night if used in open arc lamps last two
weeks in enclosed arc lamps.
The lower carbon, when removed from the lamp chimney of the last
experiment, served as a lead pencil to write on paper. The positive carbon
would not make a mark on paper. In all arc lamps carbon is distilled from
the positive pencil, condensing upon the negative pencil as graphite, which

is the material used in making "lead" pencils.
They are called "lead" pencils because they
were originally made of lead, but now they are
made of graphite which is mined from the earth.
As soon as the arc is broken it becomes evident
that the positive carbon has been heated much
the hotter of the two, a fact that could not be
detected while it was lighted because of the
dazzling brightness of the arc. The negative
carbon turns black almost immediately, while
the positive carbon remains at a bright red heat
for some time.
This fact needs to be borne in mind when
adjusting arc light carbons in search-lights,
stereopticons, and all like apparatus in which the
light must be placed at the focus of a lens. That
is, it is necessary to know from what point the
light really comes and it is necessary to have
some adjusting device to keep this point
continually at the focus of the lens. Fig. 101
24. Search-Light.—(Fig. 102). This is simply an
arc lamp with reflectors behind it and lenses in front of it. The whole
apparatus is pivoted so as to be easily made to shine in any direction. The
function of the lenses and the reflectors is to collect stray rays of light and
send them all out in the same direction. This is shown in Fig. 103 where for
simplicity the lens is represented as a single piece. L represents a point of
light which will naturally send its rays out in all directions as the radii of a
sphere; m, m, m represents a bright reflecting surface which is given that
peculiar curve called a parabola. It has the unique faculty of reflecting in a
parallel direction all the rays which may fall upon it from L, so long as L is
kept at that particular point called the focus, a b is a lens of glass which has
that peculiar curve that enables it to bend all rays which fall upon it from L,
so that they may pass out parallel.
25. Stereopticon.—This also has the necessary devices to gather the rays of
the arc lamp and send them forth parallel, and in addition it has a series of

lenses which produce upon a distant screen an
enlarged picture of any transparent object held
in these parallel rays.

Fig. 102

Fig. 103

26. Burglar's Flash-Light.—There are
many forms of this. The one we examined
is represented in Fig. 104. We unscrewed a
metal ring at the left-hand end and found,
first a glass lens and behind that a Fig. 104
miniature electric light, requiring three
volts and half an ampere. We knew,
therefore, that it must be supplied with two cells, since one cell may give
not more than 1.5 volts. We also knew that it would only be used to flash a
light, since if dry cells are required to furnish half an ampere continuously
they soon run down. Behind the lamp there was a bright metal reflector—
the lens and reflector are fairly well represented in Fig. 103. The filament of
the lamp is connected with two small battery cells in the handle. These may
be removed and replaced by new ones by unscrewing a cap at the right-
hand end. The circuit is closed by a metal spring on the side of the tube,
which acts as a push button. It is situated where it may be conveniently
pressed by the thumb. The small batteries necessarily have a short life and
must be replaced quite frequently. Being a special thing they cost nearly
twice what the regular dry cell does.

27. Mercury Vapour Lamp.—This is an
interesting variety of arc light in which the
vapour of mercury takes the place of the
vapour of carbon. G, in Fig. 105,
represents a glass tube from which the air
has been exhausted. The wires of the
lighting circuit are fused into the ends of
the tube. At one end, and in contact with
one of these wires, is a small pool of
mercury. By pulling the cord c the tube is
tilted on the pivot p, so that a stream of
mercury flows along the whole length of Fig. 105
the tube and closes the electric circuit.
When the tube falls back into its normal position, as represented in the
figure, the electric arc persists upon the mercury vapour. Incandescent
mercury vapour gives light strong in green, blue, and violet, but deficient in
red and yellow. It, therefore, gives nothing its natural appearance but casts a
ghastly hue over everything.
This lamp was invented in 1902, by Peter Cooper-Hewitt, grandson of the
founder of Cooper Union in New York City.
It gives a very suitable light for making photographic prints, and is much
used for that. This lamp operates upon the 110-volt circuit. It is the longest
step yet taken toward getting light without heat, but perhaps shows what we
must expect when we reach that goal, namely, unsatisfactory colour values
in the light. Probably such is the case with the firefly.
28. The Moore Light.—In 1896 Prof. D. McFarland Moore brought out his
vacuum tube light (Fig. 106). We visited an ordinary dry goods store which
had been equipped with this. Glass tubing is put together very much as one
would put up a stove pipe or a job of plumbing. The joints are fused and
made air-tight by playing a flame upon them after the pipe is up in place.
This pipe is led around into all nooks and corners where there would be
dark places. The air is pumped out of this tube and a trifling amount of
some vapour is introduced, the kind varying according to the tint of colour
which is desired.

Metal terminals are fused into the ends of
this tube. The tube we saw was seventy-
five feet long. A 1000-volt alternating
current is applied to the terminals and the
vapour becomes incandescent, filling the
whole tube full of light. The first thing that
the boys remarked was that although the
room was brilliantly lighted no object cast
a shadow. It seemed as though light was
everywhere and there was no chance to
screen it off. Fig. 106
29. The Nernst Lamp.—In 1897 the Nernst
lamp appeared in Germany. It is a good illustration of an insulating
substance becoming a conductor when heated to a high temperature. The
"glower," as it is called, is composed of one or several short rods of clay-
like material. This is first heated by sending the electric current through
resistance wire placed directly underneath it and connected in shunt with it.
When it gets hot, current begins to pass through it, and is automatically cut
off from the resistance coil. The glower produces an intensely bright and
white light although it does not itself exceed the temperature of 1742
degrees.
Electric installations are now so carefully constructed that fires from poor
insulation are very rare. Less than one fire in three hundred appears to be
traceable to that cause.
30. Electric Welding.—Nothing is more common in electrical matters than
heat produced by poor contacts. In this laboratory are two chandeliers, each
controlled by a wall switch. After the current has been on the chandeliers
for half an hour you will always find one of those wall switches warm,
while the other is not perceptibly warmer than other objects in the room.
The explanation is that there is poor contact in one of them. When two
metal conductors touch one another at a mere point the electric current, in
passing from one of these conductors to the other across such a narrow
bridge, meets resistance and develops heat—sometimes heat enough to fuse
the point, and either break the contact, or, what is more likely, start a minute
arc at that point. In some cases this makes the apparatus dangerously hot,
and in other cases it bridges the gap with a broader and better contact—a

true electric weld. Electric welding is applied to everything, from chicken
fence to railway rails. Enormously large currents are used for the purpose,
in some cases as high as 50,000 amperes being employed. The rails of
railroads are welded end to end by a current of several thousand amperes
sent through the joint by perhaps two or three volts. The joint heats and
fuses together merely because the poor contact offers resistance to this
enormous current.

IX

LIGHTING A SUMMER CAMP BY
ELECTRICITY
ummer had arrived. The Science Club had held its last meeting for the

S season. Harold had engaged three other boys to spend the summer at
the farm. I had the roof of an old mill reshingled and gave it to them for
a camp. They were to make it over inside. I sent the boys to the country as
early as it was possible for them to get away. It would be six weeks later
before I could follow them.

Fig. 107

When I did arrive I found they had elaborate schemes indeed. The first floor
of the mill had been partitioned off into rooms, as shown in diagram (Fig.

107), a, b, c and d being bedrooms; e was a wash room, the like of which
has never been seen before. It had not occurred to me that the mill pond m,
which came to the very corner of the building, would furnish the boys a
complete system of city water-works. At g, in the corner of this room, they
had cut a hole in the floor and nailed slats across upon the under side of the
timbers, making a depressed floor for a shower bath. This was directly over
a stream of water which issued from the mill pond. Hanging from the
ceiling over this spot was the nozzle of a garden hose. The other end of this
hose ran into the mill pond. The nozzle was capable of delivering either a
stream or a shower, according to which way it was twisted in its socket. It
was also capable of shutting off entirely the flow of water. The boys asked
me to hold my hand in the shower, and to my astonishment it was warm.
"What, pray, is your heating system?" I inquired. They invited me to go and
see. Moored outside in the mill pond at the corner of the building was our
motor boat, which the boys were allowed to use freely and which they
understood as well as any one.
They said that ordinarily they used for the
shower the cool water of the lake, which
they much preferred, and which ran of its
own accord, the lake being a trifle higher
than the nozzle of the shower, but knowing
my antipathy for the cold bath they had
slipped the end of the rubber hose over the
outlet pipe of the pump which served to
cool the gasolene engine in the boat. The
engine uncoupled from the propeller was
heating and pumping water for my shower
bath, and I immediately accepted the
invitation to enjoy it.
Certainly no bath was ever more delightful
than that one, coming, as it did, at the
Fig. 108 close of a hot, dirty ride from the city.
I had hastened the bath, because it was
already dusk and I had no candle at the mill, but suddenly the room lighted
up as if by magic. I saw then what had before escaped my notice, a
miniature electric lamp, six-volt, two-candle-power, tungsten, such as are

used for tail lights on automobiles. Since tungsten requires about 1.25 watts
per candle-power it was a 2.5-watts lamp, and since it was adapted to six
volts it would take about four tenths of an ampere.
6 volts × .4 ampere = 2.4 watts. The little wire filament looked to be about
1.5 inches long. Its resistance must have been 15 ohms.
6 volts/15 ohms = .4 ampere.
A battery of five cells was used to furnish electric current for the lamp.
Lamps were installed in the bedrooms also and were not intended to be used
more than half an hour at a time. Dry battery cells are excellent for this
purpose, and for so small a current the cheapest dry cells are as good as the
more expensive ones. These cost fifteen cents a cell. They were connected
by short pieces of bare copper wire; No. 18 "in series," as shown in Fig.
109. A wire ran from the central (carbon) binding post of one cell to the
marginal (zinc) binding post of the next cell. This battery was placed on a
shelf in a convenient place. A bare copper wire, No. 18, was attached to the
carbon post at one end of the battery and another to the zinc post at the
other end of the battery, and these two wires ran to all the rooms where
lamps were placed. The wires were fastened up on the walls by staples,
taking care that they should nowhere come in contact with each other and
"short circuit" the battery. Whenever it was necessary for one wire to cross
another, small pieces of pasteboard were tacked up to prevent their touching
each other. The lamps L (Fig. 109) were connected to these wires "in
parallel." They cost forty cents apiece, and the miniature sockets, into
which they were screwed, cost five cents each. One of these sockets was
screwed to the side of the door casing in each bedroom. Wires were
attached to the line wires, simply by twisting them together. One of these
came down to one side of the socket and the other came to the other side of
the socket through a switch, s, made of a strip of sheet zinc. The cost of the
entire installation was as follows:
5 dry cells at 15c .75
5.2 cp., 6-volt tungsten lamps at 40c 2.00
5 miniature wall sockets at 5c .25
Wire, etc. .20
——
$3.20

Fig. 109

Suppose each lamp is used thirty minutes a day for 100 days, making a total
of fifty hours. There are five lamps, making a total of 250 lamp hours. Each
lamp takes .4 of an ampere, making a total of 100 ampere hours. The lamps
are operated at six volts, making a total of 600 watt hours.
100 days
.5 an hour each day
——
50 hours
5 lamps
——
250 lamp hours
.4 ampere for each lamp
——
100 ampere hours
6 volts
——
600 watt hours

This amount of electrical energy would cost six cents if generated by a
dynamo. It is generally stated that electricity costs fifty times as much if
generated by battery as by dynamo. In this case the battery actually did
serve for the whole season of 100 days and was not exhausted at the end of
the season.
Indeed, since that season, the boys have found that battery cells which had
been too much exhausted for use on the engine served very well on the
lamps. By use the cells lose, not much in voltage, but in the ability to
furnish sufficient quantity in amperes to make the hot spark required for
igniting the mixture of gasolene and air in an engine cylinder. When they
have been discarded for use with the engine they may still furnish the small

amount of current required for the lamps—provided not too many lamps are
used at one time.
The dynamo current is always surprisingly cheap when compared with that
produced by a battery, but, on the other hand, we are never as economical in
the use of the dynamo current as we are with that of the battery.
If all five of the lamps in the above equipment were lighted at the same time
and kept burning for half an hour, the battery would run down rather badly
and would not fully recover. But if one only is used at a time and for not
more than thirty minutes, or if more than one is used at a time and for a
proportionately shorter period, the battery will receive no damage.
Dry battery cells may be purchased for either twenty-five cents or fifteen
cents each. The chief difference is that the former are capable of giving
larger current than the latter, when working against very small resistance.
For example, the former may give twenty to twenty-five amperes on a short
circuit, that is, connected directly with the ammeter without other
resistance, while the latter may give not more than six to ten amperes under
similar conditions. For most purposes, other than igniting gasolene engines,
in which dry cells are used, an exceedingly small current is required. The
electric bell, for example, may not require more than .2 of an ampere and
that intermittently. Now it is found by experience that the dry cells which
are only capable of furnishing on short circuit six to ten amperes will last
quite as long in bell work as one which may give on short circuit twenty to
twenty-five amperes. Hence it is good economy to buy them.
"What a fine sitting room you have here! (Fig. 107, f.) When do you expect
to fit it up?" said I. Instantly reminding myself, however, that boys do not
want a sitting room, I inquired what they intended to use this fine, large
room for. They told me that they had plans for making a machine shop out
of that. The idea had been suggested by a counter shaft which still hung
from the ceiling, and they had discovered that the old mill wheel would still
roll over if the penstock were repaired. I replied that I would see what could
be done about that sometime.
On the next day matters concerning the motor boat engaged our attention.

X

HOW ELECTRICITY FEELS
hat is more fickle and yet more fascinating than a motor boat? On the

W morning after my arrival at Millville the boys wanted me to go out
with them in the motor boat on the mill pond, as our beautiful little
lake is called.
Each one took a hand at trying to start the boat, but although she had acted
perfectly well the day before, on this morning no one could get a single
explosion. The switch was closed. The gasolene was turned on. The
carburetor valves were set at the mark. The spark coils responded with their
familiar buzz. She had been primed and, when she had refused to respond to
this treatment, the pet valves were opened and the wheel rolled over several
times to sweep out the cylinders. But absolutely nothing moved her—
neither coaxing nor gibes. Suddenly some one rolled the wheel over for the
five-hundredth time and she started and behaved well all day.
All this would not have given us the slightest aggravation if we could only
have found out what was the matter and what it was we finally did to
correct it. But this we shall probably never know, and hence we are
worshippers of the motor boat while we continue to distrust it and complain
of it.
While the boat was running one of the boys noticed that a binding post at
the end of one of the spark plugs seemed to be loose. He inadvertently put
out his hand to tighten it and received a terrific shock. This raised the
question among the boys, why one gets a shock from some of the binding
posts in the electrical equipment but not from others. I suggested that we
run in and call at the house to get my portable measuring instrument (Fig.
110) and a little lunch, and then go up to the upper end of the lake and take
our time in examining the electrical equipment of the boat.
The engine had two cylinders. There were two batteries—one for each
cylinder. Each battery consisted of five dry cells like the one represented in

Fig. 111.
"Now, why don't I feel the electricity when
I touch the binding posts of this dry cell?"
inquired one of the boys as he handled one
of the cells which we had taken out. "Well,
I'll give you two reasons why do you not
feel it," said I. "First, because you were
touching only one binding post at a time.
You must touch both of the binding posts
of the battery cell at the same time, so that
the electric current may pass from one post
to the other through your body. Second,
even when you do touch both binding
posts at the same time you feel no current,
simply because you offered probably about
100,000 ohms of resistance to the passage
of the current and inasmuch as the one cell Fig. 110
exerts only 1.5 volts of pressure, it could
send only about .0000015 of an ampere
through you. This you cannot feel.
(1.5 volts)/(100,000 ohms) = .0000015 amperes.
"I now connect my instrument as a volt meter between
the binding posts of the cell and you see it indicates
1.5 volts, and when I connect it for an instant as an
ammeter you see it indicates twenty amperes. That is
twice as much as they use for executing criminals by
electricity. So you see if you could reduce your
resistance sufficiently this one battery cell might kill
you. Some people have less resistance than others. The
resistance of the body is chiefly in the outer skin. If
one's hands are dry and his skin has been made tough
and horny by hard work, he has many times the
resistance of one whose hands are moist and whose
skin is thin and tender.
Fig. 111

"Suppose we select the tip of the tongue as the portion of the body which
will offer the least resistance and will be most sensitive to slight electric
currents. Let us then connect one dry cell with the ammeter and place the
tip of the tongue between the bare ends of the wire at T (Fig. 112).
"I have connected the ammeter so that it will
indicate thousandths of an ampere, and you see
that the needle moves only slightly. We cannot
call it more than .001 ampere." Each boy in turn
tried sending the current through his tongue and
each tried to tell how it felt. One said it tingled,
another said it felt warm, another said it tasted
sour and the other said he did not feel or taste
anything. "Well," I said, "whether you feel Fig. 112
anything or not one-thousandth of an ampere is
passing through your tongue and you are offering fifteen hundred ohms of
resistance.
(1.5 volts)/(1500 ohms) = .001 ampere
"Your hand offers nearly seventy times as much resistance as your tongue.
Suppose we try increasing the voltage, or pressure, of our electric current.
We will connect in series the ten cells, making a battery which you see by
the volt meter gives fifteen volts of pressure. We now find that having ten
times the pressure it sends ten times as much current as formerly through
the tongue."
(15 volts)/(1500 ohms) = .01 ampere
Each one now testified that the battery sent all the current he cared to take
through his tongue. If they send one thousand times as much as that through
a criminal no wonder it kills him. It produces a twitch when the contact is
first made, afterward a decided sensation of warmth and acid taste.
If we should increase the voltage tenfold more, say the 110-volt dynamo
current (direct current), and touch the bare conductors with our hands, the
ammeter would indicate about .001 ampere. That is, although this current
has about seventy times as much push, or voltage, as a dry cell, no more
electricity passes through the fingers than did through the tongue in the

preceding experiment with one cell. The fingers offer so much greater
resistance.
By wetting the fingers and pressing them firmly upon the bare wires, we
may make the ammeter read .01, that is, we may increase the current
tenfold by reducing the resistance to one tenth. But there is nothing
disagreeable about the feeling. If the same experiment is tried with the 110-
volt alternating current, although the quantity of current which passes
through the fingers is the same as before, the tingling is more perceptible
than in the case of the direct current. If we join together seventy-five dry
cells, giving a voltage of 112, and press the bare wires with our wet fingers,
the ammeter will indicate .01, but there is no tingling sensation, merely a
slight warmth. The battery current, being continuous, causes no twitching of
the muscles while the contact is closed. The direct current dynamo furnishes
a slightly pulsating current. Hence, one may tell by the feeling whether an
electric current comes from a battery or a direct current dynamo. The
alternating-current dynamo gives a surging of electricity back and forth in
the wires, and this may be distinguished from the direct current by its
feeling; when, however, the number of alternations per second is increased
very greatly, one may receive through the body considerable quantities of
electricity without feeling it. With a very high frequency current one may
put himself in circuit and light a 16-candle-power lamp without any
disagreeable sensation.
The outer skin is our chief insulation. If it is dry and well toughened by
work it offers a resistance of over 100,000 ohms upon gentle contact. A
wounded spot, or places like the tongue with moist, thin skin, may offer a
resistance as low as 500 ohms. If one has a pin prick or a splinter in his
hand which he cannot locate, he may hold one bare wire of a 110-volt
alternating circuit in one hand and move the other bare wire about on the
suspected region, and know when it reaches the spot by a tingling sensation.

Photograph by Helen W. Cooke
Feeling Electricity

One may touch lightly the 220-volt direct current and scarcely note any
difference between this and the 110-volt direct current, because one is not
very sensitive to the difference between .001 ampere and .002 ampere
passing through his body.
(100 volts)/(100,000 ohms) = .001 ampere,
and
(200 volts)/(100,000 ohms) = .002 amperes

Physicians treat certain ailments by the use of the electric current. For this
purpose they invariably use a pulsating or alternating current and reduce the
resistance by using metal handles and wet sponges for contact with the skin,
but even so a very small amount of current passes. The moderate twitching
of the muscles seems to be the end sought.
Men who are supposed to be killed by electric shocks often die from other
causes. A man perching upon an electric light pole, repairing wires, may
come in contact with a wire charged, say, to 2000 volts. He may receive a
shock which throws him in an unconscious condition across another live
wire which burns its way into his flesh, or he may fall to the ground and be
killed by the fall. A workman may hold a tool so as to short circuit a current
through it, making it red hot in his hands. So many men who have been
shocked into unconsciousness by high voltage currents have recovered
consciousness later that we cannot say how much current is required to kill
a man. For the execution of criminals 1800 to 2000 volts are used, and by
special metal contacts ten to fourteen amperes are forced through the body.
The first execution of a criminal by electricity was performed in Sing Sing
Prison, New York State, in 1890. There was at that time a hot controversy
among experts over the question whether death, or merely unconsciousness,
could be produced by electricity. To be on the safe side the legislature
passed a law requiring that the electrocution of a criminal should be
followed immediately by the dissection of his body. Only six states out of
forty-nine have thus far adopted that method of capital punishment, five
have abolished capital punishment, and thirty-eight still prefer hanging to
electrocution. But it should be remembered that it is amperes, not volts, that
kill. One often hears the meaningless expression, "he received 2000 volts
into his body." The volts indicate the pressure, analogous to pounds per
square inch of water pressure. Amperes of electricity are analogous to
gallons of water. It is possible to have exceedingly high voltage of
electricity without amperes enough to do damage. When one holds his
finger near to a rapidly moving leather belt and a stream of sparks passes
between the finger and the belt, the voltage may be 50,000 or even 100,000,
but the quantity in amperes is too small to do any damage or even produce
much sensation. A similar thing is true when one produces sparks by
rubbing a cat's back, or lights the gas by a spark produced by rubbing the
feet upon a carpet. Such sparks are miniature lightning discharges. The real

lightning does damage because it furnishes quantity, measurable in
amperes, as well as extremely high volts of pressure.
At this point I was reminded by the boy who had received a shock from the
engine that morning that he had touched only one binding post. How then
had he closed a circuit through his body, and how could he receive such a
terrible shock when there were only a few battery cells to produce the
electric current. I replied that he had the distinction of having encountered
about a 5000-volt current. In the language of the newspapers he might say,
Took 5000 volts and still live. We must next proceed to show how he really
did close the circuit and how the spark coil enables a battery of a few dry
cells to produce exceedingly high voltages.

XI

THE ELECTRICAL SPARKING EQUIPMENT
FOR A GASOLENE ENGINE
nder the shade of a great sugar maple, with Millville Lake spread

U before us, we took apart and examined the entire equipment for
producing the electric sparks to explode the mixture of gasolene and
air in the cylinders of our motor boat. The engine has two cylinders. For
each cylinder there is a separate battery and spark coil. Inasmuch as the
electrical outfit is duplicated for each cylinder it will be necessary for us to
consider the case of one cylinder only.
When this engine is running, 700 explosions per minute are produced in
each cylinder. In one-twelfth of a second the following four events take
place:
1. The cylinder is swept clear of the products of combustion formed by the
last explosion.
2. Four drops of gasolene are vaporized and mixed with one quart of air and
pushed into the cylinder by the pressure of the atmosphere.
3. This mixture is compressed by the piston in the cylinder to about one-
fifth its original volume.
4. The mixture is heated to its kindling temperature, which is above 2000
degrees. It then burns with a sudden expansion, which drives the piston
before it and pushes the crank which is concealed in the lower end of the
cylinder half-way around. The crank is attached to the shaft, which carries
the fly-wheel upon one end and the propeller wheel upon the other end. The
momentum of the moving parts—chiefly that of the fly-wheel—suffices to
accomplish the remaining half of the revolution.
That any machine could be devised which could repeat these four events
700 times a minute was unthinkable a few years ago.

The first men who thought that a gasolene engine could be a practical thing
were considered visionaries, but now they are found to be more practicable
than steam engines. They are so efficient that they compete with the steam
engine upon its own ground, and, in addition, they have opened up regions
of usefulness which the steam engine can never exploit. So far as we can
see, they have a permanent monopoly of the navigation of the air.
It is with the fourth event mentioned above, viz., kindling the explosive
mixture, that we are now concerned. The high temperature required for this
is obtained by forcing an electrical current against resistance.
Five dry battery cells would very readily heat a
short piece of fine wire to a sufficiently high
temperature to explode the mixture, but it is
impossible to alternately heat and cool a wire
twelve times a second. It is too slow an
operation. The only other method known at
present is to imitate the lightning and force an
electric current against the resistance of the air
with sufficient power to produce the required
heat. This, however, requires an extremely high
voltage—at least 5000 volts, and our battery of
five cells has not more than seven and a half
volts of pressure. The interesting question then
is, how does the spark coil enable us to raise the
voltage from 7 to 5000.
To help toward an understanding of the matter I
took seven small wire nails which I found in the
boat—they were sixpenny finishing nails. I then
took two or three yards of No. 24 insulated
magnet wire, such as is used upon electric bells,
etc. I use it more often than any other wire, and
always have some about the boat. I fastened one
end of this wire to one of the binding posts of a
dry cell (Fig. 113), a, and attached branches c
and d to it. The other end, b, was left free to act
as a switch for closing the circuit by touching it
to the remaining binding post.

One boy then touched the Fig. 113
bare ends c and d to the tip
of his tongue, while I touched
repeatedly the binding post with
b. There was, of course, no
sensation. We now wound a
portion of the wire upon the
bundle of nails, laying on about
fifty turns. (See Fig. 114.) The
tongue was now placed at T and
b was touched a few times to the
free binding post. A very decided
shock was felt, not while the end
of the wire was resting upon b,
but at the instant of touching and
again at breaking the connection.
The shock was noticeably
stronger at the instant of breaking Fig. 115
than of making the connection.
There was also a spark formed when the connection
Fig. 114 was broken, which did not appear before the coil was
made. We next wound on more of the wire—about
fifty more turns (Fig. 115). When now connections were made and broken
at b the tongue at T felt a much more decided shock, and a larger spark
occurred at b when the circuit was broken. Both the tongue and the spark
indicate that the voltage is creeping up very rapidly in this series of
experiments. We next connected two cells in series, then three, four, and
finally five cells in place of the one. The spark grew larger and "fatter," as
the boatmen say, with each addition of a cell. It was not pleasant to use the
tongue in the experiment after the number of cells exceeded two. I removed
the branch d from the wire b and connected it to the binding post, as shown
in Fig. 116. I then removed the crystal from my watch and poured into it a
little gasolene. I rubbed the ends of b and d together over this, and when
they separated the spark which was produced would not light the gasolene.
We had made a coil which produced a spark that looked like a miniature
flame, but still was not hot enough to set fire to gasolene vapour. It simply
needs more iron in the core and more turns of wire about it. Bringing the

ends of the wires together and separating them is somewhat like drawing an
arc with the arc light carbons. It requires a vastly higher voltage to make a
spark jump across an air gap than it does to lead it across thus.

Fig. 116

The kind of coil we have made (only larger) is very much used in houses as
a gas-lighting coil (to be described later). It is very much used also for
exploding gasolene engines. It generally passes under the name of the
"make and break" coil. The revolving shaft of the engine is made to push
together the ends of the wire and separate them at the right instant to make
the spark for explosion. Of course this is done inside of the engine cylinder.
That type of coil does not offer resistance enough to protect the battery, and
dry cells soon run down if used with it. The coils that we have in this boat
are somewhat different from that, the details of which we cannot now
entirely explain.
They offer enough resistance to cut the current required of the battery down
to one third what the "make and break" coil would take and at the same
time they raise the voltage so much higher that the spark will jump across
an air gap without being led across as an arc. Hence they are called "jump
spark" coils.

It will be remembered that when we were studying the
dynamo we produced an electric current by moving a
magnet. We may now add that an electric current may
be produced by simply changing the strength of a
magnetic field. The coil that we have just made creates
a magnetic field in the region about itself whenever a
current is passing through it. The tongue at T (Fig.
117) detects an extra current while the magnetic field
is being produced, or while it is dying away, or it will
detect any slight variations in the strength of the
current which produces the magnetic field. It is
customary to distinguish between these two currents.
The battery current which produced the magnetic field
is called the primary current and the current which is Fig. 117
detected by the tongue is called the secondary current.
The primary current in our experiments had only a few volts of pressure,
from one to seven. The secondary current had many volts, as indicated by
the spark. If we rub the end of the wire c across the binding post under b
(Fig. 117) no spark occurs. The current does not in this case go through the
coil, and no secondary current is produced. Whenever we touch the wire b
to that post we have, in addition to the primary current which has not
voltage enough to produce a spark, a secondary current flowing in the same
wire at the same time and having voltage enough to produce a spark. The
primary current is continuous while the contact is closed; the secondary
current is momentary, as the tongue detects, and is produced only while
changes are being made in the strength of the magnetic field. We will now
take another piece of wire and wind upon the coil about two hundred more
turns, leaving this outer coil wholly disconnected from the inner one, (Fig.
118). I connect c and d, the terminals of what we may call the secondary
coil, with my measuring instrument and I connect a, one of the terminals of
the primary coil, with the battery. I then rub b, the other primary terminal
across the free binding post of the battery. At the instant of closing the
primary circuit—that is, of building up the magnetic field—a secondary
current is induced in the secondary coil, which lasts for only an instant, too
brief a time for the needle to measure it, although its motion indicates both
the presence and the direction of the induced current. While the primary
circuit remains closed—that is, while no change is occurring in the strength

of the magnetic field—the needle returns to zero, indicating no secondary
current. But when now the primary circuit is broken and the magnetic field
loses its strength, the needle indicates a momentary current in the secondary
coil and in the opposite direction from what it had been at first.
If, therefore, I rapidly make and break the
current at b I produce an alternating
current in the secondary coil. I will
connect c and d with a miniature lamp and,
resting a coarse file upon the free binding
post, I will rake the end of the wire b up
and down upon this file so that, as it
dances along upon the file, it will rapidly
make and break the primary circuit, and
therefore rapidly change the strength of the
magnetic field. You notice that the lamp
lights up moderately well. It is being
lighted by an alternating current. I move
Fig. 118 the wire a little more slowly and you see
the flicker of the alternations. According to
the label upon the lamp it requires ten volts, and our battery could not give
that. We have therefore "stepped up" the voltage as we say and we have a
veritable step-up transformer.
In this case the primary and secondary circuits are entirely separate. It is a
familiar fact that different electric currents may pass through the same wire
at the same time without apparent conflict. We send numerous telegraph
despatches through the same wire at the same time. It is quite as easy for
several pairs of persons to telephone over the same wire at the same time as
it is for those same several pairs to carry on separate conversations in the
same room at the same time, at, say, an "afternoon tea." We may use the
same wire at the same time to carry direct and alternating currents. This fact
was first discovered in 1902 by Bedell of Cornell University.
Primary and secondary currents do not require separate primary and
secondary coils to convey them. They may or may not be connected into
one continuous coil. It is quite immaterial whether they are connected or not
so long as they are in the same magnetic field. Indeed, it seems that the field
outside of the wire may be quite as important as the wire itself.

We have now 100 turns in the primary and 200
turns in the secondary coils. Let us connect b
with c so as to make one continuous circuit of
300 turns. Let us then put a branch upon b to
connect with the battery, thus having 100 turns
for the primary circuit, and put a branch upon a
to connect with the lamp, thus having 300 turns
upon the lamp, (Fig. 119). When now we rub b
upon the file, as before, the lamp lights up more
brightly than before, indicating that we have
stepped up the voltage still higher. Varying the
strength of the magnetic field induces a
secondary current and the voltage of the induced
Fig. 119 current is determined, in part, by the number of
turns in the secondary circuit. If what we have
been saying is true we ought to be able to get these same results from an
electric bell. To test this we connected wires with a and c, (Fig. 120), and
since I knew that the secondary current at S would be too severe for the
tongue we decided to feel it with the hands. For this purpose we want a
larger surface than the wires themselves offer for contact with the hands,
and so I twisted the bare end of each wire around an iron spike. The four
boys then arranged themselves in line, joining hands, and the boy at each
end of the line held a spike in his free hand. Thus we had put the enormous
resistance of four human bodies joined in series in the secondary circuit.
When now I connected two dry cells with a and b (P, Fig. 120) the hammer
of the bell acted, like the file in the former case, as interrupter of the
primary circuit. As it rapidly made and broke the primary circuit, it
produced rapid changes in the strength of the magnetic field and thus
induced a secondary current which the boys all felt. The fact that it forced
its way through four bodies shows that its voltage was high. The high
voltage was also indicated by the spark which always occurred in the bell.
The primary circuit in this case has not more than three volts while the
secondary has more than a hundred. We have it in our power to give the
secondary current almost any voltage we choose, with this limitation each
increase in voltage necessitates a proportional sacrifice of quantity. The
watt power induced in the secondary circuit cannot exceed that contributed

to the primary circuit—indeed cannot quite equal it since there is some loss
in heat.

Suppose we operate a bell on a primary
current having three volts and .25 ampere,
that is, .75 watt. Suppose then the voltage
of the secondary current is stepped up to
fifty times three, or 150 volts. The quantity
of secondary current will be found to be
somewhat less than one fiftieth of .25 or
.005 ampere. The 150-volt alternating
current from the bell is more tolerable than
that from a 150-volt dynamo, because the
quantity is limited in the former case.
Our spark coil has a vibrator which acts
precisely like the hammer of the bell to Fig. 120
make and break the primary circuit and
thus make rapid changes in the magnetic field produced by the primary coil.
The primary coil of the spark coil is many times larger than the coil of the
bell, that is, it contains many more turns of wire. It has much more iron in
the core. We use upon it five cells instead of the two cells upon the bell. The
result of all this is that we have a much more powerful magnetic field than
that in the bell and many more watts of energy from which to induce a
secondary current. Now the number of turns employed in the secondary
circuit of our spark coil is very great, stepping its voltage up to thousands
where the bell induced hundreds.
Suppose we now repeat our experiment in which we tried to light the
gasolene in the watch crystal, using now the spark coil of the boat instead of
our small "home-made" coil. In Fig. 121, B is the battery of five dry cells. S
is a switch. V is the vibrator, which, like the hammer of an electric bell,
makes and breaks the primary circuit. Of course the coil has a core of iron,
although that is not here represented, and, of course, the coil has many
hundred turns instead of the few here represented, and of course also it is
built up of many layers instead of one as here represented. The secondary
has very many more turns than the primary, but those in which the primary
current passes are common to both circuits. There is also a condenser—not
here represented, and not to be described in this book. The result of all this
is that the secondary circuit has a voltage of between 5000 and 10,000, and
a spark jumps across the gap at c between one sixteenth and one eighth of

an inch long. This spark is hot enough to
light the gasolene which I have put in the
watch crystal at c.
Let us
return to
the bell
for a few
minutes. I
have here
a
miniature
lamp
which
requires Fig. 121
10 volts
and .1
Fig. 122 ampere, that is, 1 watt, which I will
connect at S (Fig. 122). When now I close
the primary circuit with two cells at P you notice that the lamp lights up,
but faintly. It is not receiving .1 ampere. Remember we have only .75 watt
at our disposal and this lamp requires 1 watt. Hence it is getting only three
quarters enough energy. We connect in a third cell and now it lights up to
full brilliancy. The resistance of this lamp must be about 100 ohms.
(10 volts)/(100 ohms) = .1 ampere
The resistance of the four boys might have been 60,000 ohms, and the
voltage of the secondary circuit might in that case have been, say, 150.
(150 volts)/(60,000 ohms) = .0052 ampere
How does it happen that the secondary current had a pressure of 150 volts
on the boys but cannot supply even the 10 volts required by the lamp?
Perhaps we can be brought to appreciate the answer to that question best by
asking ourselves some others quite like it.
Why did not the man who built our mill two generations ago locate it upon
the small stream that flowed near his house? The small stream was more
conveniently located for him and it has quite as much fall as he got at the

foot of this lake. We sometimes express the fact by saying that the "head of
water" or the water pressure was quite as much in one of these cases as the
other.
One boy said that the stream sometimes gives out. Another one said that it
never did have water enough to run that wheel. "Undoubtedly the trouble is
with the quantity," said I, "but I want to show you that we cannot maintain
the pressure unless there is sufficient quantity back of it."
In Fig. 123, suppose A represents a small,
slim tank of water three feet high. The
water-wheel W, requires one gallon of
water a minute pushed along by a three-
foot head of water pressure to run it. The
supply pipe S is bringing into the tank not
more than one quart of water per minute. A
gate at R enables us to regulate the flow of
water, as we regulate the flow of
electricity, by using more or less
resistance. Now it is evident that if we
close the gate, or partially close it, and
allow the tank to fill with water, we may
then open the gate and run the wheel for a
Fig. 123 short time, but the level of the water in the
tank soon begins to fall and the pressure
grows less and the wheel stops moving. It is just so with all generators of
electric current. If we take from them more than they can supply
continuously the voltage falls. This is notoriously true of dry cells. Like the
water tank represented in Fig. 123, they "run down" if used continuously to
furnish, say, one ampere of current, but they may furnish it for a short time,
the voltage rapidly falling meanwhile. Then if given a short rest they "pick
up" and will again furnish full pressure. The voltage of a dry cell falls
somewhat when it is required to give the very small amount of current
required to actuate a volt meter, say .015 ampere. Hence, our volt meter will
not quite correctly show what the voltage of a single cell would be on open
circuit. Notice that, when I put one cell upon this volt meter the needle
shows 1.42 volts; but when I put four cells in series upon it the needle
indicates six volts, as nearly as we can read it. That is, the voltage of each

cell in this case appears to be 1.5. What has increased the voltage of a cell
from 1.42 to 1.50? Simply this: when .015 ampere, the amount required by
the volt meter, was taken from one cell it reduced its pressure, but when a
multiplier with ten times the resistance was added we secured our reading
by using only .006 ampere of current, and this did not appreciably reduce
the true pressure of the cells.
The induced current from our bell when held back by 60,000 ohms of
resistance in the four boys was able to push with 150 volts of pressure, and
.0025 ampere passed without noticeably reducing this pressure, but when
the same current was held back by only 100 ohms in the filament of the
lamp nearly forty times as much current passed, and the pressure dropped to
something less than ten volts.
"We will try an experiment to show how the voltage will suddenly fall when
we reduce the resistance of your four bodies.
"Fill these two empty tin pails in which
our lunch was brought with water from the
lake and sprinkle in the salt left over from
the lunch. Now twist a bare copper wire
around the bail of each pail and connect
these with the bell so as to get the induced
current from its magnet. (See Fig. 124.)
Let the two pails of water be the terminals
of the two wires at S. Now you four boys
wet your hands in the water and then join
hands, and those at the two ends of the line
put your free hands upon the outside of the
pails of water while I close the primary
Fig. 124 circuit. You of course feel the current just
as you did when you held the spikes in
your hands in a former experiment. But now you two end boys put your free
hands into the salt water, and you instantly get a very smart shock. The
resistance is no longer 60,000. It has dropped way down to 2000, and if the
voltage had remained at 150 you would have received a terrible shock, but
the voltage has dropped down to five. It is as though you had been pushing
very hard against a post and it suddenly gave way. You cannot push against
a thing which offers no resistance. So the voltage falls when resistance is

reduced, and particularly if the source of supply has very little capacity.
Here is another experiment you must try when you go back to the city. At a
certain water faucet in my laboratory the pressure is disagreeably high. The
water flows with great force and spatters badly. We can easily reduce the
pressure so that the water will flow in a limpid stream. Fig. 125 shows the
situation; f is the faucet, and in the pipe underneath the sink there is a stop-
cock c. This may be adjusted permanently so that the faucet f will act
pleasantly. The same thing is represented again at the gas stove. Let f in the
Fig. 125 represent a gas cock at the stove. Suppose the pressure is so high
that the gas flames pass more gas than is readily consumed. It is possible to
adjust a stop-cock like c further back in the pipe so as to produce hotter
flames, get rid of the poisonous fumes of half burned gas, and cut down the
monthly gas bills one half.
"My garden hose will usually throw a stream across the street, which is very
desirable when one wishes to sprinkle the street, but this pressure is
disastrous when I wish to sprinkle the flowers. Turning down the stop-cock
at the nozzle makes it shoot a smaller stream but more spiteful in pressure,
knocking the flowers to pieces and washing the soil away from their roots.
But if I partially close the stop-cock at the side of the house where the hose
is attached I may have the stream of water flow as gently as I choose.
"I should meet precisely the same situation if I tried to ring an ordinary
electric bell by a 110-volt current, and I should use the same method of
overcoming the difficulty.
"The great virtue of the dynamo is that it can furnish a large supply so that
the voltage is kept constant on a great flow of current.
"I have not forgotten the question, but have tried to work toward its answer
all this time. The question is, why did Ernest get a shock this morning when
he touched only one binding post, and when the battery of five cells is not
capable of giving shocks to any one who touches its binding posts directly?
We need one more diagram to give the final answer. In Fig. 126 e represents
the binding post from which the shock was received. B is the battery of five
cells, C is the spark coil, G is the engine cylinder, f is the spark plug. When
one wishes to start the engine he closes the switch S. This makes a
continuous conductor from the battery to the metal cylinder itself. As the
engine rolls over it closes the gap in the conductor at d for an instant. The

primary circuit is then completed and the current
passes from B to the cylinder, through the metal
of the cylinder to d, then to the coil C, where it
passes through a portion of the coil and then
back to the battery. The vibrator on the coil
causes the magnetic field to rapidly vary in
strength. This induces a secondary current in the
whole coil which, because it passes through a
very great number of turns, has a high voltage.
This passes from C through B to the base of the
engine, then up the walls of the cylinder to the
plug f, then jumps across the gap at a, causing
the spark which explodes the mixture of
gasolene and air in the cylinder. The spark plug f
is porcelain—an exceedingly good insulator.
Through the centre of this passes a wire from a
to e. The current passes up this and back to C.
Now the engine rests upon the floor of the boat,
and Ernest stood upon the same floor. The wood
of this floor when dry and clean is a very good
insulator, but when wet, and particularly when
wet with water that has ever so slight an amount
of any salt in solution, it becomes a conductor
for such high tension currents. When therefore Fig. 125
Ernest, standing upon the floor of the boat,
touched the binding post, e, this induced current of high voltage found it
about as easy to pass from the metal of the engine cylinder through the
wood to his body and through his body to e as to jump across the short air
gap at a. There are two things upon which he may congratulate himself.
"1. While the coil stepped up the voltage so high it reduced the available
quantity of the current, so that the shock was a safe one.
"2. He received only a portion of the current which passed. The major part
of it passed across the gap at a, otherwise we should have noticed that the
engine missed an explosion when he touched the binding post."
The only part of this electrical outfit from which one may receive a shock is
that line from e to C. The greatest difference in electric pressure is always

to be found between the two extremities of
the electric generator; as, for example,
between the carbon end and the zinc end
of the battery, the positive and negative
poles of the dynamos; the right-hand and
left-hand end of this coil. Since the right-
hand end is connected by good conductors
with the metal of the engine and with the
floor of the boat and through it with our
bodies, we are in the same electrical
condition as the right end of the coil; but
the left-hand end and the wire connecting
it with e are forced by the varying
magnetic field into a very different state of Fig. 126
electric tension, and it is insulated from the
engine and from us by the porcelain spark plug. We say that the "difference
in potential" between the two sides of this system is 5000 to 10,000 volts.
The water in this lake flows through the stream at the other end of the lake
to the ocean. The water of the ocean evaporates to form clouds. Clouds drift
over the land and drop their rain to replenish the lake. The difference in
water level between this lake and the ocean is twenty feet. A difference in
water level is what makes it a water power and it is what occasioned the
building of our mill. This difference of water level corresponds in our
electric generators to the difference in potential. The difference in potential
maintained by our battery of five cells when not producing current is 7.5
volts. The difference in potential between the two ends of our coil, when the
battery is agitating its magnetic field, is perhaps a thousand times as much,
or 7500 volts.
The boys took their swim in the lake and afterward, while we were all on
shore lying on the grass, they brought up again the question of the machine-
shop. They were anxious to know if I had any plans in regard to it. I said I
had been thinking about it a good deal over night but had been waiting to
hear their plans. Well, they thought it would be good to have a turning lathe,
but could not think of anything else unless it might be a grindstone run by
power. I said I had thought of a Central Station Electric Plant. At this they
all sat up.

"Hydro-electric stations are the proper thing now," I remarked. "On the Rio
Grande River in Colorado they are constructing several plants where water
power will be utilized to generate electricity for use more than one hundred
and fifty miles away. For transmitting electricity to such a distance they step
up the voltage, or electro-motive force as it is called, to 100,000 volts.
They are harnessing the Au Sable River in Michigan to generate electricity
and transmit it at 135,000 volts e. m. f. to towns nearly two hundred miles
away. Electricians use e. m. f. for electro-motive force, just as you boys use
"exams." as slang for the motive force in school.
Of course we are aware that since 1896 some of the water power of Niagara
had been converted into electric power to run street cars and factories and
furnish electric light and electric heat as far away as Buffalo, twenty-six
miles distant.
About $18,000,000 are now being invested in hydro-electric enterprises
even in Mexico.
By this time the boys were all standing up and staring at me, while Harold
inquired if I were talking in my sleep. "I have at any rate succeeded in
waking you all up," said I, "and what I have said is not altogether a joke.
Let me explain somewhat at length."

XII

ELECTRICITY FROM CENTRAL STATIONS
arge dynamos generate electricity very much more cheaply than small

L machines can, and machines which have a full load continually produce
the current very much more cheaply than those which run upon very
light load part of the time. The largest central stations with load evenly
distributed for the whole day could furnish electricity profitably at four
cents per kilowatt hour. There are many small electric lighting plants which
furnish current from sundown to midnight only at fifteen cents per kilowatt
hour, with little profit. The transformer (Fig. 127) makes it possible to
gather all this generation of electricity for sparsely settled districts into large
central stations, located sometimes far away from the consumer perhaps,
where there is abundant power in some water-fall, thus saving the expense
of coal for running the dynamos.

Photograph by Helen W. Cooke
Operating the Switchboard

A few years ago there were no central stations for this purpose. Now
according to the latest census reports there are in the United States about
30,000 plants, including those which belong to certain cities, that generate
electricity for sale, and there are twice as many more isolated plants to
furnish light and power in factories, hotels, etc.
The money invested in central station business now exceeds six billion
dollars, and the annual output of electric current is sufficient to keep eight

billion 16-candle-power carbon filament
electric lights burning continuously night
and day. All this has more than doubled in
the last five years. Central stations are now
furnishing about five times as much
current for heating, cooking, and charging
automobiles as they did five years ago.
About one third of all the central stations
depend on water power.

Fig. 127

Fig. 128

Fig. 129

We might take as the type of hydro-electric central station, that is, one
which generates electricity by water-power, the Glenwood Station of the
Central Colorado Power Company. This station has two 9000 horse-power
water turbines. Each water-wheel drives an alternating-current generator
which develops 4000 volts of e. m. f. These water wheels and generators are
shown in Fig. 129. The penstocks are to be seen coming through the back
wall of the building. They bring water at 170 foot head, or about seventy-
five pounds per square inch static (standing) pressure. Three huge
transformers, each weighing twenty-six tons, step up the e. m. f. from 4000
to 100,000 volts. These are the cylinders shown in Fig. 130. They simply
contain a great many coils of copper wire with a vast amount of iron at the
centre. They accomplish in a large way what our spark coil does in a lesser
degree. But why go to all this expense to produce such a dangerous and
troublesome voltage? The answer briefly is, that while it is dangerous and
troublesome the expense is not so great as it would be to supply by any
other method the electric current required. Denver and numerous other
places, large and small, require electric current. From one to two hundred
miles away on the Grande River, there is vast power running to waste. We
have to choose on the one hand between buying power in the shape of coal
and distributing power plants to those various localities where electricity is
needed, and on the other using this water-power, which is now running to
waste, to generate electricity which we may transmit and distribute

throughout the one hundred and eighty-five miles to Denver, Leadville,
Boulder, Dillon, Idaho Springs, etc. But electric energy transmitted a long
distance suffers great loss.

Fig. 130

Suppose, for instance, I needed to supply fifty amperes at one hundred-volt
pressure ten miles distant from the generator, and had a conductor the size
of a trolley wire to bring the current. The resistance of the trolley wire is
one ohm for every two miles, or five ohms. The drop in voltage is found by
multiplying the amperes of current by the ohms of resistance. Ten miles
from the central station, therefore, the drop on fifty amperes would be 50 ×
5 = 250 volts. It would, therefore, be necessary to maintain a pressure of
350 volts at the generator to deliver the fifty amperes at 100 volts. The

energy supplied by the generator is 350 volts × 50 amperes = 17,500 watts
= 17.5 K. W. The energy delivered to the consumer is 100 volts × 50
amperes = 5000 watts = 5 K. W. In order to deliver fifty cents' worth of
electricity per hour to the consumer it would, in this case, be necessary to
generate $1.75 worth of electricity at the central station. That is, about
seventy per cent. of the energy generated would be wasted in transmission.
If now we decide to generate this electrical energy at ten times as high
voltage it will be necessary to transmit only one tenth as many amperes, or
five. In this case the drop in voltage would be 5 amperes × 5 ohms = 25
volts. It would be necessary to maintain 1025 volts of pressure at the
generator to deliver to the consumer the five amperes at 1000 volts = 5000
watts. That is, to deliver 5000 watts in this case we must generate 1025
volts × 5 amperes = 5125 watts, and less than 2½ per cent. of the energy
generated would be lost in transmission.
If now the consumer must have his energy delivered at 100 volts, we must
introduce a step-down transformer at his end of the line which may give
him 50 amperes at 100 volts = 5000 watts. This transformer, being small,
will cause a loss of 15 or 20 per cent., but if there were a very large amount
to transform it might be done with a loss of only 4 per cent.
It is not
thought to
be
advisable
to raise
the
voltage at
the
generator
higher
than
4000.
This will
not
suffice to
supply
large

Fig. 131 working Fig. 132
currents
to a greater distance than about six or eight miles. For a distance of 10 miles
6000 volts are desirable; for 50 miles 30,000 volts; for 100 miles 60,000
volts; for 165 miles 100,000 volts; and for 200 miles 120,000 volts. Notice
that in this table the voltage rises at the rate of 600 per mile. Since it is not
desirable for the generator itself to produce a higher voltage than 4000, we
must depend upon transformers to produce these high voltages. Let us then
consider, a little more in detail, the construction of a transformer. I have
here some drawings of one which I propose that we make in the machine
shop, and use in our central station equipment in the future. We will procure
the thinnest and softest sheet iron possible and cut out of it a lot of pieces
shaped like the letter H with the dimensions shown in Fig. 131. These are to
be piled one upon another, with strips of paper between, until the pile is 1½
inches thick. Then four pieces of board are to be bolted to the sides of these
(Fig. 132). The dimensions of each of the four blocks, is to be 7½ inches
long by 3 inches wide by 1½ inches thick. Upon the cross bar of the H we
will wind 400 turns of No. 12 double cotton-covered copper wire, bringing
out the ends for future attachments, and then wind on 1200 turns of No. 10
double cotton-covered copper wire. The wire will fill the space between the
blocks as indicated by the diagram in Fig. 133. We will then cut strips of the
sheet iron 6 inches long by 1¼ inches wide, and bridge across the ends of
the H, prying open the leaves of sheet iron and tucking them in between as
shown in Fig. 134. We shall then drill a hole at each corner and bolt them in
place. Binding posts will be placed at a, b, c, and d (Fig. 134), and the two
ends of the No. 12 wire will be brought to a and b and those of the No. 18
wire will be brought to c and d. Going through all this detail of construction
has probably made you lose sight of the essential features of this
transformer. Let us for a moment turn back and see what they are. We have
a large coil of wire 3 inches long and 7½ inches in diameter. It is composed
of a coarse winding and a fine winding, which we may designate as the
primary and secondary coils, if we choose. Of course the only reason for
having different sizes of wire is so that we may send larger currents through
one than the other. The coil has a laminated iron core, that is, it is composed
of layers of sheet iron. These layers are insulated from one another. This is
essential, although we cannot explain why now. But perhaps the most
essential feature of the transformer is that iron extends clear around from

one pole of this electro-magnet to the other. Fig. 135 represents a section
through the coil made in the plane of e f g (Fig. 134). The core of the
magnet is represented as heavily shaded. The magnetic circuit is said to be
closed from one pole of this magnet to the other through the strips of iron
which pass across the ends and down the sides of the coil. The arrows show
the path of the magnetic circuit. The dotted portion shows where the copper
wire may be supposed to have been cut across. Inasmuch as the electric
current is induced in the secondary circuit by continually varying the
strength of the magnetic field as much as possible, the alternating current is
the most desirable to use in the primary. If the direct current were used an
interrupter would be necessary, which would of course produce too much
sparking when any but low tension currents are used in the primary circuit.
The most interesting and curious fact about the transformer is that the
voltages of the primary and secondary currents are in exact proportion to
the number of turns in the wire of the two circuits.
In our
transform
er the
number
of turns
in the coil
between
the
binding
posts a
and b is
400 and
the
number
of turns Fig. 134
Fig. 133
between c
and d is
1200. If now we connect a 112-volt alternating current with the binding
posts a and b, a volt meter connected across between c and d will show 336
volts, and if b and c be connected by a short wire, bringing in 1600 turns
into the secondary circuit, a volt meter connected across between a and d
will show a voltage of 448. Or if, leaving b and c still connected by a short

wire, we connect the 112-volt alternating
current to a and d a volt meter connected
across between a and b will show 28 volts,
or if connected between c and d it will
show 84 volts, and if finally the 112-volt
current is connected to c and d the pressure
between a and b will be 37⅓.
The story,
then, of
the
central
station
which we
have
chosen as
a type is
briefly
this:
Fig. 135
Falling
water
makes dynamos revolve, generating a
4000-volt alternating current. This current
Fig. 136 is sent through the primary windings of
transformers. The secondary windings of
these transformers have twenty-five times as many turns as the primary
coils. This steps up the voltage from 4000 to 100,000, making it necessary
to send only one twenty-fifth as many amperes over the lines as would be
required at 4000 volts, and reduces the loss in transmission to nearly one
twenty-fifth. At the other end of the line the current traverses the secondary
windings of transformers, and the consumer receives his current from
primary coils which may step the e. m. f. down to any required volts of
pressure, generally 110.
Now I shall be glad to have you consider whether this suggests any
practicable problems for us here in Millville.
The sun is nearly setting and I suppose the family is expecting me home.

Fig. 137

XIII

ELECTRICITY FROM AN OLD MILL
illville is only a name or rather a reminiscence. There was once a

M village here, but now its population has all gone with the tide down
the river, even its ghost appears to have departed. The ruins have all
fallen, except the mill, which we propose to revivify.
I had built a summer cottage on the shore of the lake, about one mile from
the mill. The absolute stillness of the place charmed me when worn out by
the noise and heat and dirt and smell of the city. Here even the owl twittered
softly as if afraid to disturb the silence.
The silence which was such a boon to me seemed to be oppressive to the
younger members of the family. To prevent therefore their becoming
dissatisfied with the place and wishing to go to other resorts, I planned to
have some of their best friends spend much of the summer with us, and I
encouraged their plans for making use of the mill. I will not offer this as an
excuse for introducing electricity into a sleeping valley. Indeed, electricity
has always disported itself there in the lightning, jumping from cloud to
mountain peak as I have seen it nowhere else on earth.
The next time I saw the boys they had ambitious plans indeed. The penstock
at the mill was to be repaired. The water-wheel was to drive an alternating
current dynamo. The voltage of this current was to be stepped up by a
transformer. It was to be transmitted to the cottage and there the e. m. f. was
to be stepped down again by another transformer. My wife suggested that if
it interfered with the simple life it would have to step down and out. Harold,
however, assured his mother that they were going to simplify everything—
even the subject of electricity.
Their plans were: To light the cottage by electricity; introduce a number of
electric back logs, with coloured glass bottles; heat the fireless cooker by
electricity; pump the water for the house by electricity; run mother's sewing
machine by electricity; run the washing machine and wringer by electricity;

heat sad irons by electricity; percolate coffee, wash dishes and run the
vacuum cleaner by electricity; operate the door bell and the telephone and
wind the clock by electricity. I was sure that if they carried out these plans
they would stay in Millville at least that summer, so I said go ahead.
We fixed the penstock. The boys estimated that 10 cubic feet of water per
second would pass through it. They said that a cubic foot of water weighed
62.5 pounds and 10 cubic feet weighed 625 pounds. They said it fell at the
rate of 7 vertical feet a second, making 4375 foot-pounds per second. But
550 foot-pounds per second is one horse-power, hence this is about 8 horse-
power. Since one horse-power is equivalent to 746 watts of electricity, we
have, if we could generate it without loss, said the boys, nearly the
equivalent of 6 kilowatts of electricity, or about 54 amperes at 110 volts.
There were several things they wanted to know before they could go further
with their plans.
1. How many of these electrical appliances we would be likely to use at one
time.
2. How much current each device would require.
3. How much they must allow for losses in generating the current, in
transmitting it, and in transforming it.
We assured them that we would never use more than twenty amperes, say,
two thousand watts at one time. They might install a fuse, or circuit breaker
in our line to protect their plant against a greater load from us. I told them
that they might allow 20 per cent. loss of energy at the dynamo in
converting water-power into electric-power.
I would suggest generating their current at 115 e. m. f. and stepping it up to
460 for transmission to us, and then stepping it down to about one hundred
and ten volts for our use. They might count on about one-third loss on our
supply, that is, they would need to generate about three thousand watts in
order to deliver us 2000 watts.
I suggested making our line of No. 6 copper wire, which has a resistance of
two ohms to the mile. The distance from the mill to the cottage is one mile,
and the complete circuit therefore would require two miles of wire, or four
ohms of resistance.

If we start with 3000 watts and lose 14 per cent. in transforming we shall
have 2580 watts to transmit. If the voltage has been stepped up fourfold
there will be about 5.6 amperes to transmit which will suffer a loss of 22.4
volts in passing through four ohms of resistance on the line. The loss in
transmission will be about 5 per cent., and we shall have on arrival at the
cottage about two thousand four hundred and fifty watts with a voltage of
437.6. If now in stepping this down to one fourth the voltage, viz., 109.4,
we lose 14 per cent., we shall have left something over two thousand one
hundred watts, or nearly twenty amperes.
Assuming that you are able to generate 4800 watts of electricity and that
3000 watts must be furnished for transmission to the cottage, you have left
1800 watts, which will give you something over fifteen amperes at 115
volts for use in your machine shop. I suggest that we get a dynamo which
will generate both alternating and direct current—the alternating current
you will send to the cottage, and the direct current you will have for use at
the machine shop.
But how is it possible for a dynamo to generate both alternating and direct
current at the same time?
Recall that all dynamos are
generators of alternating
current. If the brushes rest
upon rings upon the axle
they send forth alternating
current—but if the brushes
rest upon commutator bars Fig. 138
Fig. 139
they send forth direct
current. Now we will have two sets of brushes, one pair of
which shall rest upon the rings on the axle, and they will collect alternating
current for the cottage, while the other pair will slide over the commutator
bars and collect direct current for the machine shop. I have constructed a
model which will make it plain. Here is a piece of a broom handle (Fig.
138), one foot long, which shall represent the axle of an armature. a b c d is
a stout wire which represents the coil of the armature. In this case it has no
iron at its centre. Nevertheless it will serve as an armature having one loop
of its coil left. e and f are rings, sawed from a piece of brass pipe, which fit
snugly upon the axle. Another ring of the brass pipe was sawed lengthwise,

as shown in Fig. 139. These two halves are also fastened upon the axle and
one end of the wire loop, c, is fastened to one of these, and the other end of
the loop, b, is fastened to the other half of the ring. These two halves of the
piece of brass pipe are placed so that their edges are near to each other but
do not touch on either side of the axle. The two ends of this wire loop are
also connected with the rings e and f. A short wire connects b and e and
another connects c and f passing through the wood of the axle, as shown by
the dotted line. We will now revolve this loop slowly about its axle in a
strong magnetic field. To produce this field I will send two amperes of
electricity through the coils of wire (Fig. 140), which surround two iron
pole pieces that are screwed into an iron base. Between the poles N and S of
this electro-magnet we will thrust this wire loop and revolve it as an
armature very slowly. Meanwhile I connect two wires to my sensitive
ammeter and let their free ends brush along on the rings e and f. The needle
of the ammeter swings to and fro for each half revolution of the armature,
showing an alternating current of .01 amperes. If this armature had many
turns of wire instead of this one loop, if it had an iron core, and if it should
revolve at high speed, the results would differ in degree but not in kind.
We will now move the wires which are
acting as brushes over to the metal pieces
b and c. When now we revolve the
armature the needle swings to the right,
and just as the needle is about to swing
back each brush slides from the plate on
which it is rubbing to the opposite one and
the needle gets another impulse forward. If
the armature is turned rapidly the pulses
disappear and the needle stands constantly
at about .015 amperes. This then is both an
Fig. 140 alternating and a direct current dynamo. It
simply needs more iron, more copper wire,
and more rapid motion, to give us the 4800 watts of electrical energy we are
seeking.
"But how shall we produce the current which we wish to send around the
spools of the field?" inquired the boys.

"Connect the field with the brushes which rub upon the commutator," I
replied. "It will magnetize its own field."
As good luck would have it, we found that the ledge of rock which
furnished the basis for the mill dam was immediately underneath the floor
at the north end of the machine shop. Upon this we built up a solid
foundation for the dynamo. Our water-wheel gave a speed of 240
revolutions per minute to the counter shaft. A pulley of two feet in diameter
upon this counter shaft was belted to the pulley of one foot in diameter
upon the dynamo—thus giving its armature a speed of 480 revolutions per
minute. We had to fix a governor upon the water-wheel to keep this speed
constant at varying loads. The voltage is very sensitive to slight changes in
the speed of the generator.
We had next to plan what equipment we should need for the machine shop
and to decide where to locate each machine. The first machine we installed
was a lathe adapted for use both with metals and wood. Among the adjuncts
of this were all sorts of drills, chisels, circular saws, grinding and
burnishing tools, etc. The second machine located was a small forge with an
electric fan to furnish the blast. These were followed by a small band saw
and a small planer. The fifth machine was a big grindstone and the sixth
was an emery wheel. The boys had a long discussion, running through
several days, on the question whether these machines should be belted to
the counter shaft, and thus get power directly from the water-wheel, or
whether each machine should be operated by an electric motor attached to
it.
Harold said: "Suppose I want to saw a piece of wood requiring a horse-
power, I must start an eight horse-power water-wheel which will run a six-
horse-power dynamo which will operate a two-horse-power motor that will
revolve the saw. There is a loss in each machine, and the lighter the load the
greater the loss. In order that the motor may deliver one horse-power to the
saw, it must receive from the dynamo, say, one and one-half horse-power,
and in order that the dynamo may deliver to the motor one and one-half
horse-power, it must receive from the water-wheel, say, two horse-power.
What is the matter with my saving time and energy by sawing off the block
with my own right arm?"

"But," said Ernest, "you forget that this water-wheel and the dynamo must
run all the time by the terms of our agreement with the cottage, and they
will run fairly well loaded, so that the starting of the saw will not entail any
such losses as you reckon. Furthermore the water-power is running to
waste, anyway. You simply divert its channel when you start all this
machinery. That's all. And lastly, if the saw requires a horse-power, as you
say, your right arm could not furnish it."
"Oh," interposed Dyne, "it would take a horse-power to do it as quickly as
the machine does, but Harold simply proposes to take more time in sawing
the block and less in running the machinery. An infant can do the work of a
horse if you give him proportionally more time."
"I don't like the idea," drawled Erg, "that this machinery has got to be kept
running all the time. When will a fellow get a chance to sleep or go a-
fishing or have any vacation, with this central-station machine shop on his
hands all the time?"
I had inquired how the last two boys won their nicknames of Dyne and Erg
and had been informed that one was very keen about dining and the other
had a great aversion for work. They had doubtless seen these terms
somewhere in their reading of physics, but they appeared to have forgotten
their significance by a too familiar use of them. I told them that these were
sacred terms, the first being a name for the unit of force, while the second
designated the unit of work. Both boys said that under those circumstances
they would like to shed the names. The names, however, stuck and the boys
themselves might, I think, be said to exercise a maximum of power with the
least waste of energy.
This idea of running the plant continuously had evidently received no
attention hitherto and it bid fair to quench all the enthusiasm until I came to
the rescue by proposing a storage battery.
If we can procure a battery in which we may store energy, which shall
always be on draught by merely pushing a button, one which "is not injured
by overcharging nor too rapid discharging, nor even by complete
discharge"; one which is not injured by standing idle for any length of time,
either charged or discharged; and finally one which "is practically
foolproof"—we want to try it. I propose that you appoint a committee to

look into it. But at any rate this enterprise must go on even if I have to hire
a man to live in the loft of the mill and keep the machinery going.

Fig. 141

"No man in the loft," said Dyne, "while I have my rations."
"There will be no need for him so long as I can store energy here," said Erg,
"so let the job of equipping the establishment go on in the regular fashion."
After a long confab one evening at the mill we settled upon the arrangement
shown in Fig. 141. D represents the location of the doors and W that of the
windows. The equipment is designated as follows: A, saw; B, planer; C,
lathe; E, emery wheel; F, grindstone; G, dynamo; H, forge; I, storage
battery; J, switchboard; K and L, counter shafts suspended from the ceiling.
The water-wheel is belted directly to the counter shaft L. This revolves at
the rate of 240 r. p. m. A two-foot pulley on this shaft is belted to a one-foot
pulley on the dynamo G, giving the dynamo a speed of 480. A 4-inch pulley
on this counter shaft is belted to a 16-inch pulley on the grindstone F,
giving the stone a speed of 60 r. p. m., or one revolution per second. A 32-
inch pulley on shaft L is belted to an 8-inch pulley on the counter shaft K,
giving a speed of 4 times 240, or 960 r. p. m. 12-inch pulleys on this shaft
are belted to 6-inch pulleys on each of the machines A, B, and C, giving
them a speed of 1920 r. p. m., and a 16-inch pulley on this shaft is belted to

a 4-inch pulley on the emery wheel, giving it a speed of 3840 r. p. m. As
soon as everything was in running order, Harold took his mother down to
the machine shop and started all the machinery going at once, and while
they stood in the middle of the room I heard him explaining to her how she
might find out the speed of each machine. He said that she must start with
the grindstone, because that goes slowly enough to count. She held her
watch in hand and counted the number of revolutions in a minute, as he
directed, and found them to be sixty. Then he asked her to judge how much
larger the pulley on the grindstone was than the corresponding one on the
counter shaft. She said that she thought it looked four times as large. He
told her that she had it just right, and explained that the shaft must move
four times as fast as the stone, or 240. "Now how fast do you think the
emery wheel is going?" She acknowledged that she had no idea.
"Well," said he, "when you get real used to it you can tell by the tone a
wheel makes just about how fast it is going."
Then he explained how she might calculate its speed by looking at the
pulleys, and she found that the counter shaft was going four times as fast as
the shaft L and that the emery wheel was going four times as fast as K.
Hence it was going sixteen times as fast as L, or 3840 r. p. m. His mother
said she thought that it was fascinating to stand in the middle of the room
with the slowly moving grindstone on one hand and emery wheel moving
sixty-four times as fast on the other hand and think that they were propelled
by the same water-wheel. I handed Harold a speed indicator which I had
just received, (Fig. 142), the mechanism of which was all visible. Harold
looked at it for a minute and found stated upon it that the wheel B had 100
cogs, and he very quickly inferred that the axle A, whose screw threads
fitted into these cogs, must revolve one hundred times each time the wheel
B revolves once. The tip end of this axle had a soft rubber cap C. Without
suggestion from me he soon held this rubber shoe against the end of the
axle of the emery wheel and counted, not thirty-eight, but thirty-six
revolutions of the wheel of the speed indicator in one minute. This puzzled
him and he inquired how it happened that the emery wheel made only 3600
rather than 3840 revolutions per minute.
"Well," said I, "we always have to count on belts slipping some, particularly
upon very fast moving pulleys and upon very small pulleys. Here are two
belts to slip, and still you are losing only the effect of one revolution of the

counter shaft L in a minute. Grind
something on the emery wheel and you
will find that the belts will slip more. In
fact, grinding upon the emery wheel will
compel the water-wheel to go more slowly
until its governor opens and gives it more
water. The water-wheel makes fifteen
revolutions per minute and the emery
wheel goes 256 times as fast as that. One
Fig. 142 pound of resistance at the emery wheel is
like 256 pounds of resistance at the water-
wheel. You notice the same thing when you use the saw or planer, or even
present a chisel to a piece of soft wood in the turning lathe.
"The only machine here that it is important to keep running at constant
speed is the dynamo. We shall probably notice the dimming of our lights at
the cottage every time you saw a block or grind with the emery wheel or
even polish with the felt buffer, because the speed of the dynamo will
slacken for a moment and the voltage will drop a little."
In addition to sending electric current to the cottage the dynamo was to
keep the battery stored all the time. Each machine had an appropriate motor
attached to it which could run it by drawing current directly from the
battery when the water-wheel was not running. Thus if one wanted to
sharpen his pocket knife he merely closed a switch at the lathe and used the
small stone, or if he wished to sharpen his lead pencil he put it in the lathe
and applied a chisel to it.
These motors were all adapted to the 110-volt direct current and the battery
contained fifty-seven cells, each cell being rated a little under two volts.
The boys frequently discussed possible combinations in this system. I spent
a great deal of time loafing around among them in a comatose condition,
and they talked quite as freely when I was around as when they were alone
among themselves. One day I heard Dyne say, "Suppose we should store in
a reservoir the water which comes down the penstock during a day and
store all the electricity it will generate in a day in a storage battery, then at
night let the battery run the dynamo backward as a motor, and that turn the
water-wheel backward as a rotary pump, we should have the water in the

upper reservoir to begin work with the next morning and the problem of
perpetual motion would be solved.
"Aw, why do you want to do all that," said Erg, "when nature is doing it for
us?"
Ernest said he had a better scheme than that. He would turn the battery
current on to all the motors in the room and they would run the counter
shafts forward and the counter shafts would run the dynamo forward and
the dynamo would charge the battery, and so you could keep up the motion
perpetually if you wanted to.
"Get out your pencils," said Harold, as he took down a copy of Houston and
Kennelly. "Let us see how we would come out if we tried Dyne's
proposition for, say, twenty hours, storing the energy from the falling water
for ten hours in the battery and then using this energy during the next ten
hours for re-storing the water in the upper pond. We will say that the water-
wheel furnishes eight horse-power for ten hours—eighty horse-power
hours."
I notice it is stated in this book that small dynamos are usually unable to
deliver more than 75 per cent. of the energy impressed upon them, and
storage batteries and motors deliver about 80 per cent. of the energy
impressed upon them. The accounts would, therefore, stand as follows:
Dynamo Horse-power Hours
Dr. Cr.
To energy impressed by water-wheel 80
By energy delivered to storage battery 60
By loss in heat 20
————————
80 80

(Assuming that the battery was able to receive all the dynamo could give.)

STORAGE BATTERY ACCOUNT
To energy impressed by dynamo 60
By energy delivered back to dynamo running as motor 48
By loss in heat 12
————————
60 60

Dynamo Running as Motor Horse-power Hours
Dr. Cr.
To energy impressed by battery 48
By energy delivered back to water-wheel 36
By loss in heat 12
————————
48 48

(This dynamo being a particularly inefficient motor.)

We cannot give the account of a water-wheel acting as a pump, because
such a machine has not yet been perfected. It is evident however that if a
water-wheel could be devised that should be a perfect pump, the losses in
this chain of machinery are more than half; indeed, the accounts show them
to be 60 per cent. We should, therefore, be able to return less than half the
water drawn from the lake each day, and we should rapidly move toward
bankruptcy.
"Well," said Ernest, "my proposition is more successful than that, because it
sets out to be a fool proposition."
It was first suggested by the snake who undertook to swallow himself.
Suppose the account does taper down from eighty to one, so does the snake,
but he still remains "wise as a serpent." Our account would stand as
follows:
Dynamo Battery Motors

36 27 27 20 20 15
15 12 12 9 9 7
7 5 5 4 4 3
3 2 2 1 1 .8
.8 .6 .6 .48 .48 .36
.36 .27 .27 .20 .20 .15
.15 .12 .12 .09 .09 .07
.07 .05 .05 .04 .04 .03
.03 .02 .02 .01 .01 .003

It is evident that while our energy would dwindle continually we should
never quite come out of the little end of the horn, since any number may
diminish by 20 per cent. of itself indefinitely.
"Let us get at something practical," said Erg. "How are we going to furnish
electricity to the cottage when the dynamo is not running? If we put a

storage battery at the cottage, how are we going to store it having nothing
but alternating current up there; and if we attempt to transmit current from
our central station battery, how are we going to get along with the drop in
the voltage?"
"I'll tell you how to do that," said Dyne. "They want 20 amperes and the
line offers 4 ohms of resistance. That means a drop of 80 volts. We have
simply to provide a subsidiary battery of 48 cells, which we may throw in
series with our 57 cells when we supply electricity to the cottage, and then
they will have the right voltage for use out there."
"Yes," said Erg, as he rolled over, "they will have the right voltage when
they use 20 amperes, but what will happen if they simply turn on one lamp.
The drop in voltage then will be (.5 amperes × 4 ohms =) 2 volts; 105 cells
at 1.8 volts a cell will send out there 189 volts minus the drop of 2 volts,
leaving 187 volts upon a lamp adapted to 110 volts, and it will immediately
burn out. The same thing would happen to any single piece of apparatus if
the current was turned upon it alone. The only thing they could do if they
wanted to light a lamp, say in the middle of the night to take a dose of
medicine, would be to start up all together, all their lamps, sewing machine,
wringer, dishwasher, fireless cooker, vacuum cleaner, etc., etc., to keep
down the voltage so that one lamp would not burn out."
"I have read," said Ernest, "that they use rectifiers, which convert the
alternating into direct current, for storing batteries. These are much used
over the country. Electric automobiles run by storage batteries, and in the
great majority of communities there is no other electric current than the
alternating. So they would be helpless without the rectifier. We should then
get another battery of fifty-five cells for the cottage and keep it stored by
using a rectifier with our alternating current.
"But all their equipment up there," said Ernest, "is adapted to the alternating
current. Of what use would a direct current be to them?"
"Well," said Harold, "it is all the same whether you have alternating or
direct current on lamps, cooking apparatus, etc., and I have understood that
they have motors which run on both alternating and direct currents. If so,
that would fix them up all right."

The boys now turned to me for the first time to inquire whether motors
could be obtained which would run on both alternating and direct current,
and I replied that small motors for running sewing machines, vacuum
cleaners, etc., were made which would serve us, perhaps not economically,
but as they were the only solution to our problem we could get along with
them.
"Why don't they have alternating current batteries?" inquired Erg.
"Well, it is time that we learned about the nature of batteries," said I, "if you
boys are going to have two storage batteries to care for."

XIV

DOING CHORES BY ELECTRICITY
hores were my salvation in youth, and those chores were not trifles. I

C was made to feel that the whole family depended on my milking the
cows, bringing in the eggs, keeping the wood box full of wood, the
water pail full of water brought from the old well, churning the butter,
feeding and watering the animals, and performing a multitude of regular
daily and weekly tasks. As I grew older my responsibilities were allowed to
increase proportionally so that I might feel some measure of the dignity of
being a mainstay and a support of the family. Long before I reached
manhood occasional opportunities were presented for me to play the full
part of a man. These sometimes came during a temporary absence or
sickness of my father, but more often, as I learned afterward, by his
skilfully eliminating himself from the situation so that I might try my
powers.
We attempt in the present generation to furnish a substitute for the old time
chores by our daily programme in school or in summer camp, but I often
wonder whether this round of trifles can make men. Can one grow great
without having a chance to feel occasionally that the world depends upon
what he does?
The great advantage of Millville to us all lies in the fact that my wife is a
good organizer. She immediately saw that the introduction of electricity into
the cottage enabled her to assign chores to us all. These chores were
assigned so that the establishment ran like clock-work. On Monday
morning in a large room, called the wash room, she arranged the soiled
clothes in five piles. Pile No. 1 contained sheets and pillow cases; No. 2,
white shirts, shirtwaists, and other starched clothes; No. 3, underclothes;
No. 4, towels, etc., and No. 5, coloured clothes. Here stood a washing
machine run by electric motor and a wringer run by the same motor (Fig.
143). By the side of it sat a tub for rinsing water and next to that a tub for

bluing water. Two boys placed a wash
boiler over a two-burner oil stove, put five
pails of water into it, and cut up one cake
of laundry soap which they also put in.
When this was boiling hot, about half of it
was poured into the washing machine. The
other half was to take its place later in the
washing machine. The first pile of clothes
was put in and the motor run for five
minutes. This batch was then run through
the wringer into the rinsing water, and then
again through the wringer into the bluing
water, and then through the wringer a third
time into the clothes basket, and hung
upon the line out doors in the clear
sunshine, which did more than all else to
make them sweet and clean. A basket of
such clothes from the line makes you want
Fig. 143
to plunge your face right into it and take a
good whiff. There is nothing like it except
a mow full of new hay. The piles of soiled clothes follow one another
through this series of tubs on about a fifteen to twenty minutes headway, so
that the whole family washing is done wholly by two boys inside of two
hours. Each pile after the first is given ten minutes in the washing machine.
On Tuesday the ironing is done with
electric irons (Fig. 144). On Friday the
house is cleaned by the vacuum cleaner,
run by electricity (Fig. 145).
On Saturday a lot of baking is done in a
series of fireless cookers (Fig. 146).
The sewing machine runs more than ever
before. I hear "It is such fun to sew with an
electric motor." And the electric fan which
Harold installed for his mother over the Fig. 144
sewing machine "makes that the coolest
spot in the house."

Fig. 145

Fig. 146

Fig. 147

Chores do not take all of the time, nor most of the time. They are simply the
important things which must be done right on time. Meanwhile there is
plenty of time for other things and a vast lot of experimenting goes on down
at the mill. It is my chief entertainment to stroll down there every day and
look on. One day I found this project on trial: On the floor (Fig. 148, f) of
the room over the wash room at the mill a large dripping pan A, was set on
blocks of wood so that one corner was lower than the rest. A rubber pipe, B,
brought water to this pan from the mill pond, an inverted faucet, c,
regulating the flow. The overflow from the pan fell into a funnel, d, the
stem of which went through a hole in the floor. A short piece of rubber pipe
connected this with the nozzle, e, of a gardener's sprinkling can, which hung
from the ceiling in the compartment for the shower bath. Electric lamps
attached to a board, g, were inverted over the pan of water, so that the bulbs
of the lamps were immersed in the water. The electric current for these
lamps was controlled by a switch, h, placed by the side of the water faucet.
When one wanted a shower he could have it as cold or as hot as he chose by
adjusting properly the switch and the faucet. Moreover, it was not necessary
for him to wait, for warm water flowed immediately.

Fig. 148

In discussing this the boys said that a 32-candle-power lamp used 110
watts, and that since 96 per cent. of the energy supplied to the lamps went
into heat each lamp transformed 105 watts of electrical energy into heat.
But 100 watts sufficed to raise one pint (one pound) of water five degrees in
one minute. They used seven lamps or about one horse-power, and adjusted
the flow so that the shower delivered one quart of lake water per minute
warmed for a tepid bath.
The next time I sauntered down to the mill the boys were working on what
they called an electric shower bath. They had fastened upon the wall of the
bath room an electric bell (Fig. 149), and placed on a shelf near by a battery
of two dry cells, P. The switch which closed this primary circuit was on the
wall by the side of the faucet and electric heating switch (Fig. 148). One of
the wires, S, for the secondary circuit was carried up and connected to the

pan A (Fig. 148). The other wire was
fastened to a sheet of zinc about a foot
square, which lay upon the floor of the
shower bath. The idea was that when one
was taking a shower bath, if he chose to
vary his sensations he might step upon the
sheet of zinc, close the switch in the
primary circuit and let the secondary
current pass through his body by way of
the shower. They said that it was
particularly prescribed for slow people.
Speaking of chores, of course the most
insistent chore was to keep the storage Fig. 149
batteries stored. This process gave rise to
many questions, through which the information contained in the next
chapter was brought out.

XV

ELECTRIC CURRENTS FROM CHEMICAL
ACTION AND CHEMICAL ACTION FROM
ELECTRIC CURRENTS
uigi Galvani (1737–1798) of Bologna, Italy, in 1786 unwittingly
L produced an electric current from chemical action. Because he was
eagerly seeking other results he misinterpreted this. Several words in
the dictionary are becoming either obsolete or misnomers. For example,
galvanism is an old-fashioned word for an electric current. The expression
galvanic electricity is a relic of the abandoned idea that there are several
kinds of electricity, of which Galvani discovered one. Galvanized iron is
wholly a misnomer. It is a name used for iron which has been coated with
zinc, and it suggests the idea that somehow the zinc is coated upon the iron
by means of an electric current, whereas in fact it is done by dipping the
iron into melted zinc.
Alessandro Volta (1745–1827) of Como, Italy, took up the discovery of
Galvani, interpreted it correctly, and perfected the method of producing
electricity by chemical action. What these two men really discovered was
that it is possible to produce continuous currents of electricity. Before that
electricity was known only by the instantaneous discharge or spark. From
the name of Volta is derived the word volt, which designates the unit of
electro-motive force. The adjective voltaic is synonymous with galvanic, as
voltaic or galvanic cell, voltaic or galvanic current. For a long time it was
thought that such an adjective was needed to designate electric currents
generated by chemical action as a peculiar kind of electricity. We no longer
think of electricity which is generated by chemical action as different from
that generated by a dynamo or from any other source.
For about seventy-five years after the discovery of Galvani chemical action
was our only method of generating currents of electricity, and it is largely
owing to the inadequacy of this method of production that so few uses for

electricity were discovered previous to the perfection of the dynamo about a
third of a century ago. Two things have conspired to bring about this age of
electricity. (1) The dynamo reduced the cost of production from five dollars
to ten cents per kilowatt hour. (2) Mankind grew extravagant, greatly
increased the number of things which it considered necessary, and at length
became both able and willing to spend more for the things which it
demanded.
The so-called voltaic cell is of scarcely more than academic interest now.
The school which, as a rule, follows half a century behind practical life, has
taught and still teaches the philosophy of the galvanic cell with great
particularity. It is now being urged to undertake the teaching of the dynamo.
Meanwhile the dynamo has almost driven out of existence all electric
battery cells except the storage cell and the so-called "dry cell," and each
year the dynamo is encroaching more and more upon the territory of the dry
cell. In the present day, when a passenger upon a street car pushes a button
to stop the car, he uses, not a voltaic cell, but a 500-volt dynamo current to
ring a small buzzer, and it costs the company not one-hundredth part as
much as it would to furnish him a battery equipment to do the same thing.
Small dynamos and magnetos are displacing dry battery cells in the
sparking equipment of motor boats and automobiles.
We lifted a dry battery cell out of its pasteboard case and found that it was
contained in a metal cup of sheet zinc. The top of this was sealed over
airtight with pitch, the purpose of which is to prevent this "dry" cell from
drying up. We dug away the hardened pitch and found a black powder
which was distinctly moist. In case the pitch becomes cracked or a hole
appears in the zinc cup, the moisture passes out and the cell ceases to act as
a generator of electric current.
The zinc cup had a lining of pasteboard on the sides and the bottom, similar
to the pasteboard which enveloped the outside, only the lining was quite
moist. A corrugated rod of carbon about an inch in diameter occupied the
middle of the cup, and the space around it was packed full of a mixture of
ammonium chloride, manganese dioxide, and other substances like plaster,
etc., which differ with different cells. A dry cell which has been long in use
is quite apt to show stains upon its pasteboard case. These are caused by
holes which appear in the zinc. The production of electric current by the cell
is dependent wholly upon a chemical action between the zinc and the

ammonium chloride which results in the destruction of both. This chemical
action cannot go on without moisture.
The zinc cup of the particular cell which we were examining appeared to be
intact, and we proceeded to dig out the black powder. Its black colour is due
to the manganese dioxide. Ammonium chloride is white. We lifted out the
carbon rod and scraped the zinc cup clean. The binding posts attached to
both the zinc cup and the carbon rod were left intact. Into the zinc cup we
now poured a tumblerful of water and added about a quarter of its volume
of hydrochloric acid, setting the whole into a large bowl to guard against
disaster. Bubbles of gas were formed rapidly, causing the liquid to
effervesce as a tumbler of soda water would do. We inverted an empty
tumbler over the cup so as to collect this gas. In about two minutes we lifted
the tumbler, still holding its mouth downward, and brought a lighted match
to it. There was a flash and the contents burned with a pale-blue flame.
Some of the zinc had united with some of the hydrochloric acid and set free
hydrogen gas, which is one of the constituents of the acid. This is typical of
chemical actions. Something similar takes place between the ammonium
chloride and the zinc. Three interesting things occur in this experiment:
1. Chemical action, just described, is produced.
2. Heat is produced. This was very evident when we took the zinc cup up in
our hands. It was as hot as though boiling water had been put into it.
3. An electro-motive force is produced. This we showed by connecting one
end of a piece of copper wire to the binding post of the zinc cup and the
other end of the wire to an electric bell. Another wire ran from the bell to
the carbon rod. When the carbon rod was lowered into the acid the bell
rang.
Within ten minutes holes began to appear in the side of the zinc cup. The
acid contents began to flow out into the bowl, and not long after the zinc
fell to pieces. After fifteen or twenty minutes the action began to grow less.
The acid was being used up as well as the zinc. If enough acid is added the
zinc will wholly disappear.
We have chosen substances which would produce striking results in this
experiment, but the same sort of thing is going on about us continually.

One summer by the seashore I fastened a brass plate upon my boat with two
screws—one of brass and one of galvanized iron. The plate was attached
below the water line so that it might be acted upon by the salt water. Within
three weeks the head of the galvanized iron screw had entirely dissolved,
while the brass screw was as good as ever. A galvanized iron screw near by
but not in contact with the brass was still in as good order as ever. I had
simply made an electric battery cell out of the ocean by dipping into it zinc
and brass in contact.
A most interesting relationship exists between the three kinds of activity in
the cell, which have been mentioned, viz.: (1) chemical action; (2)
production of heat; (3) production of electric current.
As has been already noted, chemical action produces heat. Conversely, if
we apply heat to the cell we greatly increase its chemical action. We have
also noted that chemical action produces an electric current, but unless the
current is allowed to flow through some external channel like a closed
circuit of wire the chemical action is greatly restrained or entirely checked.
In a glass tumbler I put a rod of pure zinc
(Fig. 150, Zn), and an electric light carbon,
C. A short wire, a, was arranged for
connecting the two externally. In the
tumbler was put some water with about
one tenth its volume of sulphuric acid. No
chemical action was evident until the wire
was touched to the zinc, closing the circuit.
Then bubbles of hydrogen gas gathered
upon the surface of the carbon rod, and
clung to it very tenaciously. We lifted out
the carbon rod and rinsed off the bubbles
in another tumbler of water, and then
returned the carbon to its place in the cell.
The experiment was repeated many times,
and each time no bubbles of hydrogen,
Fig. 150 which is in this case the sign of the
chemical action, appeared until the circuit
was closed for the flow of the electric current. Incidentally it should be said
that the amount of hydrogen produced by the chemical action is a measure

of the amount of electric current produced. Incidentally also it should be
said that the bubbles of hydrogen clinging to the carbon rod check and
almost stop both the chemical action and the production of electric current
when the circuit is closed. If now we put in sodium bichromate to use up
the hydrogen as fast as it is produced we may have a continuous current
whenever the circuit is closed. Chemical action does not entirely cease in
this cell when the circuit is opened. But if two cells are prepared, and one is
left with its circuit closed while the other remains with its circuit open, it
will be found that the zinc disappears and the acid is used up in the closed
cell in a short time, while these remain not greatly changed for a long time
in the cell on which the circuit is open. No cell will remain forever without
chemical action, yet a dry cell which might use up its zinc and ammonium
chloride in a few hours if the circuit is closed may be kept idle three or four
years, and still be able to furnish electricity enough to ring a bell. Some
persons feel defrauded if the author of a book fails to give them all the new
words and conventional terms which belong to any subject. For such here is
a page or so.
It is conventional to speak of the electric current as flowing from the carbon
through the wire to the zinc, although every one has suspicions that it may
flow in the other direction or even that it may not flow at all. It is
conventional to designate any part of the circuit from which the current
comes as positive (+) to any other part toward which it flows, this latter
being considered negative to the former and designated (-). The current is
conceived of as making a complete circuit, from carbon to zinc through the
wire and from zinc to carbon through the liquid. Hence, the binding post of
the carbon rod is called the + pole and that of the zinc is called the-pole,
while the zinc rod or plate beneath the surface of the fluid is called the +
plate and the carbon is called the-plate. The liquid is termed the electrolyte.
The sodium bichromate, introduced to cause the hydrogen to unite with
oxygen, is called an oxidizing agent or even a depolarizing agent, and
hydrogen collecting upon the negative plate is said to polarize the cell.
Hydrogen may be made to collect upon the carbon or negative plate until
the electric current reverses its direction. The hydrogen is said to be more -
than the zinc. If we connect the zinc and carbon rods with the wires
bringing an electric current from the dynamo we may make either one
positive as we choose, according to which is connected with the positive

wire. Hydrogen bubbles will collect upon whichever plate we make the
negative one.
When we send an electric current from the
dynamo into this cell it is called an
electrolytic cell, and when it is used to
generate an electric current it is called a
battery cell. In either case the electrolyte is
decomposed and put through a chemical
change, though the chemical action in one
case is the reverse of that in the other, and
the direction of the electric current in one
case is the reverse of that in the other. For
example let us consider the case of a zinc
rod and a carbon rod immersed in
sulphuric acid and the external circuit
closed. The current passes as indicated by
Fig. 151
the arrows in Fig. 151, and the chemical
actions result in hydrogen leaving the
sulphuric acid and zinc taking its place, forming zinc sulphate. This is a
white salt and for purposes of this experiment must remain dissolved in
water. So far we have been considering a generator of electricity—a battery
cell. We may introduce something at m, say a motor, which will indicate
that an electric current is flowing. At length the cell ceases to generate
current and is, as we say, "run down." Suppose now we substitute a dynamo
in place of the motor in this circuit, connecting it so that the carbon rod
shall be its positive pole and the zinc its negative pole. We now call this an
electrolytic cell, (Fig. 152). The current will decompose the zinc sulphate.
The zinc will be coated upon the zinc rod and hydrogen will be procured
from the water present, of which it is a constituent, to form again sulphuric
acid as originally.
We shall thus restore the conditions which prevailed in the first case as
represented in Fig. 151. H2SO4 is the chemist's designation of sulphuric
acid and ZnSO4 is his expression for zinc sulphate.
The experiment illustrates a storage battery so called. It might better be
called a chemical transformer.

It is wholly unnecessary that one rod be
composed of zinc. If we begin with both rods of
carbon immersed in a solution of ZnSO4, and
send into this cell the dynamo current, the
carbon which acts as the negative pole will be
coated with zinc in a short time, and we shall
have in effect a rod of zinc and one of carbon as
before. After a minute or two we may
disconnect the generator and substitute in its
place a bell as indicator, and it will ring, Fig. 152
showing that we have transformed electrical
energy into chemical energy which is now being retransformed into
electrical energy. We say that we store electricity by this means, which is,
however, no more true than that a farmer stores his farm in the bank when
he sells it and deposits the money until he shall need it to buy another farm.
Here is a very beautiful blue salt. I will drop a few crystals of it into a
tumbler of water and dip in two carbon pencils connected to the dynamo
current, using between fifty and sixty ohms of resistance in the circuit so as
to have two amperes flowing. After a minute or two I lift out the negative
carbon and you see that it is well plated with copper. The blue salt is copper
sulphate. If we weigh the negative carbon, both before and after the
experiment, we shall find that copper has been depositing at the rate of one
ounce in twelve hours. If we reduce the current one half, making it one
ampere, it will deposit copper at the rate of one ounce in twenty-four hours.
One ampere will separate three ounces of lead in a day from a solution of
any lead salt; it will separate .9 ounce of iron in a day from a solution of
any iron salt, and it will liberate from water, which is a compound of
hydrogen, one gallon of the gas in ten hours. The amount of chemical action
is a measure of the amount of electrical energy expended. Before the
present form of commercial wattmeter was devised electrolytic cells were
used to determine what the consumer's bill for electricity should be each
month. These chemical meters contained a solution of zinc sulphate for the
electrolyte and both the positive and the negative plates were of zinc. While
the current is passing, zinc from the solution is coated upon the negative
plate and zinc from the positive plate takes its place in the solution, thus
maintaining a constant strength of solution.

Here are three iron nails. I propose that you plate one with zinc and another
with copper and then expose all three to the weather and see which will
rust. I propose that you replate all the spoons at the cottage and the metal
tops of the salt cellars with silver. Electro-plating results better if done
slowly. Ten volts and .1 ampere will be sufficient current.
In the storage battery we generally use lead for both positive and negative
plates and dilute sulphuric acid for the electrolyte. Hydrogen is liberated at
the positive plate and oxygen unites with the negative plate. When the
charging current is cut off the chemical action reverses, and an electric
current is produced by the cell.
In all other batteries there is a destruction of one plate and of the electrolyte,
which cannot be fully restored by a charging current, although in the case of
the lead and sulphuric acid combination the charging and discharging of the
cell may go on alternately for a very long period without permanent change
or loss of any substance except water. There is, however, plenty of loss of
energy in this as in other transformers. One hundred ampere hours of
current expended to charge a storage battery will yield from seventy-five to
eighty-five ampere hours while the battery is discharging.
The lead storage battery is, however, full of disappointments for those who
do not properly care for it. It is irretrievably ruined if neglected and allowed
to charge too far, or discharge too far, or evaporate too much water, etc. The
voltage of a lead cell must not rise above 2.2 nor fall below 1.8. It must not
be allowed to furnish at any one time a greater number of amperes than it is
rated for. It must not stand idle too much. It must not be cleaned up and put
away for a period. In fact, the lead-sulphuric acid battery is so poorly
adapted to our need that I feel disposed to try Mr. Edison's new storage
battery. This has nickel hydrate packed in tubes of metallic nickel for the
positive plates and iron oxide pressed into pockets in a sheet of metallic
iron for the negative plate. A solution of potassium hydrate in water is used
for the electrolyte. This is said to be uninjured by being emptied out and left
idle, as our batteries must be for a large part of the year. The e. m. f. of this
battery is less than that of the lead battery, being only 1.2 volts. We shall
therefore need ninety-six cells (type B-4) for the machine shop and ninety-
one cells of the same kind for the cottage. Our dynamo will be unable to
charge at one time more than sixty of these cells connected in series.

The particular chore which you boys must perform is to see that the voltage
of these batteries is maintained at about 1.2. It should be charged up to 1.8
volt at least once a week and never allowed to discharge to a lower pressure
than one volt. The level of the electrolyte must be maintained one half inch
above the plate by adding distilled water occasionally.
A few years ago every student of chemistry was more or less agitated by the
thought that more than half of every clay bank was composed of metal
nearly as valuable, or at least as costly, as gold. This is aluminum. By all the
methods then known it was a very difficult and expensive process to extract
the metal from the clay. At length, by the perfecting of the dynamo, the
chemist had under his control great and powerful electric currents which
enabled him to unlock any chemical compound however refractory and
isolate its elements. As a result aluminum became common enough and
cheap enough for even kitchen utensils.
The metal calcium which a short time ago was an exceedingly rare
substance worth $40 an ounce is now fairly abundant and cheap for
chemical experiments, although it has no qualities which will give it an
extended use.
Powerful electric currents, such as are obtained at Niagara, enable us to
combine elements into hitherto unknown chemical compounds. Carbon and
silicon are made to unite to form carborundum, which vies with the
diamond for hardness. Carbon and calcium unite to form calcium carbide,
used with water to form acetylene gas.
In such processes the intense heat of the electric arc—perhaps 6000 degrees
—is employed, together with the electrolytic action of the current, to
separate and combine substances. Enormous currents are used in the electric
furnaces for producing chemical reactions—from 1000 to 30,000 amperes
at a time.
Electric currents passing through the human body expend their energy
partly in heat and partly in electrolysis. So simple and harmless a thing as
common salt would become a virulent poison if it could be electrolized in
the body into its elements sodium and chlorine.
Let us make use of an electric current to decompose water into its elements,
hydrogen and oxygen. I have a three-ounce wide-mouthed bottle (Fig. 153)

and through its cork I pass two short pieces of No. 24 platinum wire by
pushing a stout needle through first. I fill this bottle with pure water and cut
a slight furrow in the side of the cork, where water may drip out when the
gas is produced in the bottle. We crowd the cork firmly into the mouth of
the bottle and invert it. No water drops out. We bend the ends of the
platinum wires into hooks and hang upon them the wires bringing the
dynamo direct current. There is no evidence of chemical action. Pure water
is an exceedingly poor conductor of electricity. Let us now put about fifty-
five ohms of resistance into the dynamo circuit, so that it will pass about
two amperes, and put a very small pinch of salt into the water, which makes
it so good a conductor that its resistance may be ignored. When now we
close the circuit, as before, a brisk effervescence takes place. Bubbles of gas
rapidly form on the platinum wires and break away, rising through the
liquid. Twice as many form on the negative wire as on the positive one. As
these gases rise to the top of the bottle an equal volume of the water drips
out through the small hole in the cork.
Two amperes of electricity will liberate two
fluid ounces of hydrogen at the negative pole
and one fluid ounce of oxygen at the positive
pole, in five minutes. Hence in five minutes the
bottle should be full of a mixture of two gases,
two thirds of which, by volume, is hydrogen and
one third oxygen. We will catch the water which
drips out so that we may measure it. The bottle
being now full of gas I shut off the current, and
removing the cork I bring a flame to its mouth.
A very loud and startling explosion takes place.
We pour the water back into the bottle, and it
seems to fill it as well as before. We have
decomposed a few drops of water—not enough
to measure—into two gases, one of which, the
hydrogen, occupied two thirds of the bottle, and
the other, oxygen, occupied the remaining third.
At ordinary temperatures they would not
Fig. 153
reunite, but when raised to their kindling
temperature they united, producing light, heat, a

loud noise, and the few drops of water which had been originally
decomposed by the current.
This is the electrolysis of water. I wonder if any such chemical action took
place in Ernest's body when he received that severe shock on the motor boat
the other day.
It is significant that the "dry" battery cell must be moist in order that
chemical action may go on in it. Compare with that fact several others that
we may learn from observation, for example: Baking powders must be kept
dry to retain their strength. That is, if they get moist chemical action will
begin in them, and the gas which is one of the products of this chemical
action will pass off. Now it is the sole function of baking powders to
produce gas within the dough, and if the gas has wholly or partially escaped
they will fail to make the bread stuff "light." The same reasons obtain for
keeping seidlitz powders and other effervescing salts, such as vichy and
kissingen, dry. It is to prevent the chemical action which is provoked by the
presence of water. The same thing is true of the rusting of iron, and the
various kinds of corrosion of metals. We may prevent such action
indefinitely by keeping them dry. Berries, fruits, meats, milk, eggs, grain—
all kinds of foods—are preserved from spoiling—from chemical changes—
by drying them and keeping them dry. The same thing is true of wood,
paper, cloth, etc. A wooden fence post may last from five to ten years. A
fence rail, being less exposed to moisture, may last two or three times as
long. The interior wood of a house may last a century or two, while the
exterior wood, being exposed to the weather, may require repairs very
frequently. Shingles on the roof do not last as long as shingles on the side of
the house. Those on a steep roof last longer than those on a flatter one. A
pitch of at least forty-five degrees in a roof is desirable to keep it dry. The
north and west sides of a house being least exposed to storm in this climate
last the longer. Precious books, records, deeds, wills, etc., on paper must be
preserved in dry air. A sail will keep strong and white if kept dry.
But it is impressed upon us by our experiences that sunlight is even more
potent than moisture to produce chemical change. Photographic processes
are dependent upon the power of light to produce chemical changes. The
fading of our tapestries and our garments, the tanning of our skins, the
development of green material in the leaves of plants, all are evidently the
direct result of sunlight. A picture hung on the wall prevents the wall paper

behind it from being faded by the light, or it prevents the wood behind it
from being turned yellow by the light. Folds in our garments prevent them
from being faded all alike. Very many substances to be found in a chemical
laboratory, in a drug store, or in a kitchen must be kept in the dark if they
are to be guarded against chemical change. No experienced housewife
would let a barrel of flour or potatoes sit in the sun, and every housewife
knows that the sun is the best agent for bringing about those chemical
changes which she desires. Hence she puts her bedding, her milk pans, her
bread box, her butter jar, etc., "out to sun." She has open plumbing, that the
sun may enter those dark and dirty corners.
If you would guard a substance against chemical change, keep it in a dry,
dark place. We have come to associate the sun and the weather as
disintegrating forces. Hence the south and east sides of the building need
most frequent repairs. Every one who has made time exposures in
photography knows that the sunlight from the east is, as a rule, two or three
times as powerful as that from the west. There is less moisture and dust in
the air to screen us from the early morning sun than from the late afternoon
sun. When there is enough moisture in the air to make the sun look red,
those rays from it which would produce chemical action, called actinic rays,
are cut off. Photographic processes are then exceedingly slow. It is like
exposing a plate in a dark room behind the ruby glass.
But our daily experiences teach us that not only moisture and light but also
heat stimulates chemical action. We restrain chemical action by cold when
we put things in the ice box. We hasten chemical action by heat when we
put things on the stove. Winter restrains all the chemical activities of nature,
and summer quickens all the vegetable and mineral kingdoms into chemical
activity. If we would preserve a substance from chemical change we must
keep it in a cool, dark, dry place. Now those conditions which will favour
the chemical activity of a battery cell will enable it to produce electricity,
and those conditions which will restrain chemical action will enable us to
preserve the cell from running down.
But we have lately learned that other forms of radiation besides light and
heat exist and aid in chemical action. We may produce radiographs—
pictures on photographic plates—without light but with invisible rays,
which are akin to light and to electricity.

XVI

ELECTROCUTION AT MILLVILLE
he old mill was infested with rats. My wife laid down to the boys the

T principle that good housekeepers were never troubled with vermin of
any kind. The rats' sole occupation is to search for food. If you don't
feed them they will not stay with you. But the boys said that they were glad
of a chance to try an experiment on the rats. So one day when I went down
to the mill I found them discussing the possibility of killing the rats by
electricity. Harold said that he had read that it took much less electricity to
kill any animal than to kill a man, and he would like to try, for instance,
whether the shock which they had received from a bell would kill a rat.
"Well, who's going to sit by," said Erg, "to close the primary circuit when
the rat happens to get himself into the secondary circuit?"
"Make him close it himself by some device," said Ernest.
"They have a regular thoroughfare, a beaten highway, along by the wall,
under the mill and up through a hole in the floor of my bedroom," said
Dyne.
"Well," said Harold, "I propose an electric trap which shall have two
compartments. We will keep cheese in the inner compartment, the walls of
which shall be of wires so that the rats may see the cheese. The floor of the
outer apartment shall be covered with wire, as shown in Fig. 154. The wires
of the secondary circuit from the bell (Fig. 156) shall be fastened to the
binding posts b and c (Fig. 154). The partition d shall be a swing door into
the apartment A where the cheese is. This is shown in profile in Fig. 155. d
must act as a switch to close the primary circuit through the bell P (Fig.
156). We will have three dry cells in the primary circuit. Now this is the
way it will work: A rat comes up from under the mill with wet and slimy
feet—just suited for making contact for the electric current to enter his
body. The smell of the cheese attracts him. He circles around the trap
several times, watching the cheese in apartment A through the wire screen.

He sees a
narrow opening
into this
apartment
under the door
d. He puts Fig. 155
himself in
position upon the floor of the outer apartment B,
his feet bridging the gaps between the two
systems of wires belonging to the secondary
circuit. When he thrusts his head under the door
and pushes it, it swings in a little, bringing one
metal strip against another, which belongs to the
primary circuit. This closes that circuit. He will
Fig. 154 never hear the bell ring, for the electric current
which will shock him to death travels 186,000
miles per second, while his sensations travel
only sixty miles an hour. If the involuntary recoil of his muscles does not
make him jump back, so that the door will shut and stop the bell from
ringing, Dyne will be awakened and he will close the door, since we will
put the trap at that hole where the rats enter his bedroom."
The next night three rats were electrocuted
by this device.
I told the boys they had so many
interesting things going on at the mill that
we should have to have a telephone
between it and the cottage so that we could
talk them over.

Fig. 156

XVII

THE TELEPHONE
he telephone was the great invention of our centennial year, 1876.
T Elisha Gray and Alexander Graham Bell each claimed to have been the
inventor. It is quite probable that each did discover it independently, but
the result of the long patent suit was that the court awarded the claim to
Bell. It is, therefore, known as the Bell telephone.
Many who installed telephones during the first few years of their existence
had them taken out again as nuisances. They are far greater nuisances now
than at that time, but the necessity of them has come upon us and entirely
enslaved us.
There were more than eleven billion messages sent by telephone in the
United States in 1907. The capital invested in telephone business was
$814,616,004. The income for that year was $184,461,747. All of these
items had more than doubled during the previous five years. In 1880 there
were about eight times as many miles of telegraph wires as of telephone
wires. In 1907, there were about eight times as many miles of telephone
wires as of telegraph wires. The Bell system had 3,132,063 stations, and
independent companies had 2,986,515 stations in 1907.
The first telephone line ran from Salem to Boston, Mass. This was in 1877.
The next year the first telephone exchange was established. It was eight
years before a telephone line was extended from Boston to New York. On
October 18, 1892, the first telephone message was sent from New York to
Chicago. Previous to 1895 telephoning, like telegraphing, was done by one
wire, using the earth, as we say, to complete the circuit.
But at about that time electric car and electric lighting lines became so
common that they interfered with telephoning. These currents running in
lines parallel to the telephone wires induced currents in them, and when a
person put a receiver to his ear for conversation he heard the hum of electric
light dynamos and the buzz of electric cars so loud that conversation was

quite impossible. The next step was to introduce a return wire—the double
metallic circuit as we call it. Thus outside currents induce equal and
opposite currents in the two wires of the circuit, which neutralize each
other.
It was this same year, 1895, that the "central battery" system was introduced
into telephone equipment. This is not usually a battery at all, but a dynamo.
The price of all electrical supplies in 1895 was about one tenth what it had
been in 1885, and at the same time the goods were of far better quality.
Important telephone patents expired in this year, and immediately private
and independent lines began to be established. It was also in 1895 that the
telephone company began to use an automatic registering device which
enabled it to charge telephone rates according to the number of calls.
The boys unscrewed the end of a telephone
receiver (Fig. 157) and found inside a
permanent magnet made of several steel
bars bolted together (Fig. 158). This was
shown to be a magnet by presenting a
small pocket compass to either end. The
Fig. 157 left-hand end of this magnet proved to be
its north pole by repelling the blue end of
the compass needle.
On the left-hand end of the magnet was a
small spool of No. 36 copper wire, silk
covered. It offered 75 ohms of resistance,
and since it takes 2½ feet of this wire to
furnish 1 ohm of resistance the spool Fig. 158
contains 187½ feet. A thin disc of soft iron
.01 inch in thickness is held by the hard
rubber case very near to but not quite touching this end of the magnet. We
drew this disc to one side, as shown in Fig. 159, and connected the receiver
by wires to a magneto. We turned the crank of the magneto slowly and the
iron disk danced up and down, keeping time with the revolutions of the
armature. The magneto furnished an alternating current, which, when it
flowed around the coil in one direction, strengthened the pole of the
magnet, and in the reverse direction weakened the pole. When the crank

was turned so as to produce twenty to
thirty revolutions of the armature per
second the dancing of the disc sounded
like the low hum produced by the wing of
a humming bird. When a large, wide-
mouthed bottle was brought near to this
the sound was greatly reinforced, as the
sound of a bee becomes louder when he
appears at your open window. We next
replaced the iron disc and put on the cap
again. We then connected the receiver at S Fig. 159
(Fig. 160) and connected two dry cells at
p. When the primary circuit was closed the disc vibrated in time with the
hammer of the bell making the same tone. We substituted for the bell a
series of buzzers. The smallest had an armature about one inch long, while
that of the largest was about two inches long. The shorter the armature the
faster it vibrated, and the higher was the pitch of its tone. We arranged these
as shown in Fig. 161. A, C, D, E and F are the buzzers. B is a battery of two
cells and G, H, I, J and K are springs of sheet brass which act as push
buttons. By operating upon these springs with one's fingers, as upon the
keys of an organ, it was possible to represent the tones of a reed organ after
a fashion. The armatures are reeds and they are made to vibrate by electro-
magnets. We called it an electric organ. The telephone receiver was
connected at T, and the wires which led to it were lengthened so that the
receiver might be a long distance away. The disc in the receiver kept time
with the armature of each buzzer when it sounded and faithfully reproduced
its sound. But the strangest thing was that when any two buzzers sounded
together, or, indeed, if all five buzzers sounded together, the receiver
responded to them all at the same time, so that a person in another room or
in another house, with the receiver at his ear, might hear exactly what those
did who were in the same room with the buzzers. The wires from the
receiver were connected with the coil in each buzzer so as to get the
induced current, as shown in detail in Fig. 160.

Fig. 160

Fig. 161

We took a telephone induction coil (Fig. 162) and fastened it to a board as
represented in Fig. 163, I. One wire of the primary circuit was fastened to
the binding post a. The other wire from the primary coil passed to the
switch S and then to the battery. From the battery the wire ran to the binding

post b. C is a steel tuning fork. The
secondary circuit is closed through a
telephone receiver. These wires are
extended so that the receiver is too far
distant for the tuning fork to be heard
through the air. When the switch S is Fig. 162
closed the tuning fork acts as the
interrupter for the primary circuit, and it interrupts according to its time of
vibration. If, for instance, the fork gives the tone of middle C on the piano it
vibrates 256 times a second. It interrupts the primary circuit 256 times a
second. It induces an alternating current of the same frequency in the
secondary circuit. The diaphragm of the telephone receiver vibrates in
perfect time with the tuning fork and produces the same tone as the tuning
fork. We had a series of tuning forks giving a variety of tones, which we
could substitute one after another in place of this one. The receiver
reproduced accurately the tone of each one of them.
We took a small induction coil (Fig. 164) c
and fastened one end of the primary circuit
to a battery, B. The wire at the other end of
the primary circuit was bent into a hook h.
This hook was adjusted about a quarter of
an inch from the end of the iron core of the
coil. The other wire from the battery was
attached to the steel strings of a piano, P.
When the coil c was brought over a string
and the hook h was allowed to pass
beneath the string and touch it very gently,
the primary circuit was closed through the
string, which served as an interrupter of
the current and vibrated according to its
tone. The secondary coil, not represented
in the figure, was connected to a distant
Fig. 163 telephone receiver, which reproduced the
tones of the piano strings.
Producing a tone is merely a matter of making something vibrate with the
required frequency. It may be a piano string, or a tuning fork, or a reed of an

electric buzzer, or the diaphragm of a
telephone receiver. If it vibrates 256 times
a second, it will produce the same tone as
middle C on a piano; if it vibrates 512
times a second it will produce the C which
is an octave above, and if 128 times a
second an octave below middle C. The
human voice is produced by vocal cords in
the throat, which vibrate with the proper Fig. 164
frequency to give any required tone. But
how can we make the human voice act as an interrupter of the primary
circuit? An examination of the telephone transmitter will supply the answer
to this question.
The boys
after
taking the
transmitte
r (Fig.
165) apart
proceeded
to make
one
which
should
Fig. 165 answer
the Fig. 166
purpose
as follows: A block of wood about one
inch thick and three inches square (Fig. 166), A, was hollowed out, making
a cone-shaped cavity about one half inch deep and one inch broad. This
cavity was filled with small pieces of graphite, G, made by cutting up a lead
pencil. An old tin-type, D, was laid over this as a diaphragm and tacked
around the edges. A binding post, E, passed through the block, its head
being buried in the graphite at the bottom of the cavity. The binding post F
furnished contact with the tin-type. One dry cell was placed at B and the
sensitive ammeter was connected at C. The needle showed that although a
small current was passing it was constantly varying in strength. Tapping

upon the table, walking across the floor of the room, shouting, and
particularly whistling, caused variations in the conducting power of the
graphite and consequently variations in the current strength. This is
precisely the condition we wished to produce in the primary circuit.

Fig. 167

We next substitute for the ammeter at C the primary and secondary coil of
the telephone. In Fig. 167 T is the transmitter, B is a battery of two dry cells,
P is the primary winding of the coils, and S is the secondary winding. To
this a telephone receiver, R is connected by wires long enough to reach into
another room. A person holding the receiver at his ear could hear everything
said or done in the room where the transmitter was almost as plainly as
though he were present in the room.

Fig. 168

Two such transmitters were made and the second one was placed in the
room where the receiver had been, while a second receiver was installed
near the first transmitter. The arrangement is shown in Fig. 168. T is the
transmitter at one end of the line and T' the transmitter at the other end. B

and B' are the batteries at each end, P and P' the primary coils, S and S' the
secondary coils and R and R' the receivers. With this arrangement two
persons carried on a conversation with perfect ease, holding the receivers to
their ears, presenting their mouths to the transmitters and speaking in
moderate tones. H and H' are hooks upon which the receivers are to be hung
when not in use. These hooks act as switches to open and close the primary
circuit. A spring normally pushes the hook upward and closes the circuit,
but while the receiver is hanging upon it the circuit is open at this point.
Thus the battery is saved from running down when the telephone is not in
use.
The wires were finally extended from the mill to the cottage and this
equipment was installed at each end.
It will be noticed that the secondary circuit includes two receivers and two
secondary coils besides the wire of the lines to offer resistance.
The receivers offer 75 ohms of resistance each. The secondary coils offer
250 ohms each and the line wires between the mill and the cottage offer 100
ohms. This makes a total of 750 ohms for the secondary circuit. But the
rapid alternations which are induced in the secondary circuit impede the
electric current ten times as much as the resistance already mentioned.
When considering alternating currents passing through coils of wire we are
obliged to take into account two kinds of resistance:
1. Ohmic resistance.
2. Impedance.
"You boys understand the resistance to the flow of the electric current,
which we have so often measured in ohms. But I want to show you that
there is another kind of resistance which alternating current meets. Here is a
coil containing 1000 feet of No. 20 copper wire. I throw on to it, for only an
instant, the 110-volt direct current, and the ammeter reads 11 amperes,
showing that it offers a resistance of 10 ohms to the direct current. I now
throw on the alternating current, and the ammeter shows only a small
fraction of an ampere. The surging of the current back and forth induces a
counter electro-motive force, in the successive layers of the coil, which we
call impedance. In the experiment which we have just performed impedance
is fifty times as important a factor as ohmic resistance. Impedance depends

chiefly upon the frequency of alternation. The impedance in telephone
circuits is particularly large because of the extremely high frequency of the
alternations produced by the tones of the human voice, these being usually
not far from ten times as rapid as those of alternating currents in common
use.
"We may estimate the total resistance of our telephone circuit as equivalent
to 7500 ohms.
"Our secondary coils have forty times as many turns as the primary coils,
and by means of them the voltage is stepped up to somewhere near one
hundred on open circuit. When closed through the line, however, the
voltage drops down to about ten. The result is that the actual current which
passes between the cottage and the mill when we telephone is not far from
.001 ampere. We may, however, hear a whisper transmitted by .000001
ampere or less.
"The tone E´ which is produced by the tenth key above middle C on the
piano, is the one most readily heard over the telephone. It is produced by
anything which vibrates 640 times per second."

Fig. 169

We used No. 12 galvanized iron wire for our telephone lines. Two miles of
No. 12 copper wire would offer 16 ohms of resistance. The iron wire offers
about 100 ohms. But this is a trifle when compared with the total resistance.
We used a double metallic circuit so as to avoid the effects of inductance
from our electric lighting circuit.
The next thing that we were obliged to consider was some arrangement for
calling persons to the telephone for conversation. We decided to use
magnetos and alternating current bells. Fig. 169 shows the essential

mechanism of the bells. The bell at each end of
the line consists of two gongs a, b and a´ b´,
with a hammer c, c´ between them. This
hammer is attached to an iron armature h, h´,
pivoted over the electro-magnets, m, m´, in such
a way that it rocks back and forth when an
alternating current passes through the lines d e, f
g. The bells at both ends of the line always ring
together, since they are connected in series. A
magneto (Fig. 170) is situated at each end of the
line. This, as has been previously explained, is a
Fig. 170 generator of electricity, in which the field is
furnished by steel magnet, M. The armature A is
a coil of wire whose ends are in contact with the
leading out wires d and c by means of brushes which slide upon rings. The
armature is revolved by hand. The crank and cog wheels employed to
produce high speed are not shown in the figure. By turning the armature
rapidly this magneto will develop 60 volts e. m. f. on open circuit. The
magnets of the bells are wound with a very large number of turns of very
fine wire, so that .025 ampere is sufficient to ring them.

Fig. 171

Figure 171 shows how the magneto at either end of the line is introduced
into the circuit for the purpose of ringing the bells. B and B' represent the
bells, m and m' the magnetos, and P and P' represent switches. Springs push
them upward so that they normally close the circuit through the bells. When
a person at P wishes to call another at P' he pushes the switch P down so as
to bring his magneto m into series with the bells. When now he turns the
crank and generates the electric current, both bells ring. His own bell serves
the purpose of telling him that the line is operating all right. The other bell
calls the party desired for conversation. As soon as the operator removes his
finger from the switch P the spring throws it upward again, leaving his bell
in circuit, so that he may be called at any time, but cutting out of the circuit
his magneto, which would introduce unnecessary resistance.
The same wires which carried the current for ringing the telephone bells
carried also the current for operating the telephone receiver. When the
receiver is removed from the hook it releases a twofold switch. This serves
the double purpose of closing the primary circuit through the local battery
and substituting the telephone receiver circuit for the bell-ringing circuit
upon the line.
We used fifty chestnut poles to carry our line between the mill and the
cottage. Each pole had a cross bar, on one end of which the electric light
and power wires were carried and on the other end the telephone wires.
Glass insulators prevented the wires from coming in contact with the wood
of the cross bars. The necessity for this was impressed upon the boys by
something which happened while they were stringing the wires. The
telephone apparatus at the mill had been installed and the two leading out
wires had been connected to it. One of these was coiled up on the floor,
while the other had been strung along upon the poles for half a mile, but

had not yet been attached to the insulators on the poles. While the boys
were lunching at the mill, one of them gave the crank of the magneto a turn,
when, to the astonishment of all, the bell rang. The circuit had been
completed through the damp wood of the mill, through the damp wood of
some of the poles, and through the earth. After lunch the wire, so far as it
had been strung, was fastened to the insulators upon the poles. But when
some one turned the crank of the magneto the bell still rang. We walked
along the line to see where the difficulty was. We found the end of the line
about half a mile from the mill dangling free from the ground, but touching
a tall spear of grass. When this was moved away from the spear of grass the
magneto could no longer ring the bell. The slight current required to ring
this bell—.025 ampere—had found its way through the spear of grass,
through the woodwork of the mill and through the earth.
We had no sooner got the two telephone wires properly strung and attached
to the hundred glass insulators when a thunder storm came up, and drove us
back to the mill for shelter. Pretty soon the bell rang and we, supposing that
some one at the cottage was trying to call, went to the instrument, but could
get no response, nor could we make the bell ring. Lightning had sent an
alternating current over the line which rang the bell, but the strength of the
current was too great for our coils of fine wire and one of them was burned
out, as we say. In other words, the wire had melted at the point where it
offered the greatest resistance.
The burned-out coil was replaced, and then we installed lightning arresters
which were of two kinds. The first were simply fuses which were
introduced into the line to protect it against any current too large for the
apparatus to carry, and the second was a plate, c (Fig. 172). These are to be
found upon the top of the magneto cases. A wire is connected with c, and its
other end is grounded by being connected with a piece of iron pipe which is
driven deep into moist earth.
The plate a b is inserted in the line, and the gap between this and the plate c
offers sufficient resistance so that the telephone circuit suffers no leakage at
this point, but lightning has such extremely high tension that it readily
passes across this gap and finds its way to the earth without damaging the
instruments.

We have already noticed that our alternating current
dynamo, which produces 60 vibrations per second in
the telephone receiver, causes it to give a tone very
nearly like the C, which is two octaves below middle
C upon the piano. C requires 64 vibrations per second.
We may speed up our dynamo so as to make it yield a
tone exactly like C or even above it.
Dr. Cahill of Holyoke, Mass., has devised an organ in
Fig. 172 which alternating current dynamos produce the
necessary number of vibrations for each tone. The
name telharmonium has been proposed for this organ. It has a separate
dynamo for each tone, each dynamo having a frequency corresponding to
the tone required of it. The dynamo, for instance, which produces middle C
makes the electric currents surge back and forth 256 times a second, and
this causes the diaphragm of a telephone receiver to vibrate 256 times a
second, and this sends forth 256 air waves per second, and when these reach
our ears we recognize the tone we call middle C. The frequency of
alternation in a dynamo may be increased by either increasing its speed of
revolution or by increasing the number of coils upon its armature.
Mr. Cahill's great organ looks like a large machine shop with many counter
shafts geared so as to run at different speeds. On each shaft are a large
number of little dynamos whose armatures have various numbers of coils.
The organist, who may be far removed from this "machine shop," fingers an
ordinary keyboard. Each key opens and closes a switch, thus bringing into
action its own dynamo.
If the key which is known as C, one octave below middle C, is pressed
down, a switch closes the circuit between the telephone and a dynamo
which gives 128 double alternations of current.
The tone which is produced by 128 vibrations per second is the one most
often heard from a man's voice in ordinary conversation.
Another key brings into action upon the same telephone receiver—and at
the same time if desired—a dynamo which gives twice as many alternations
per second and produces the tone most often heard in female conversation.
It is middle C.

Another key might bring into action a dynamo which gives 64 vibrations
per second to the diaphragm of the telephone receiver. This would send
forth a tone very nearly like the base note of our 60-cycle alternating
current dynamo.
The following table shows a series of ten tones which might be produced by
the same little piece of sheet iron in a telephone receiver played upon by ten
dynamos at the same time. The whole list of ten tones would sound well
when produced simultaneously. The great mystery is that the iron disc can
vibrate in such a complex manner. It is important to note, however, that the
number of vibrations in each of the upper tones is a multiple of that of the
lowest tone:
2nd octave above Middle C C´´—1024 (= 16 × 64)
G´ — 768 (= 12 × 64)
E´ — 640 (= 10 × 64) [A]
1st octave above Middle C C´ — 512 (= 8 × 64)
G — 384 (= 6 × 64)
E — 320 (= 5 × 64)
Middle C C — 256 (= 4 × 64) [B]
G — 196 (= 3 × 64)
1st octave below Middle C C, — 128 (= 2 × 64) [C]
2nd octave below Middle C C,,— 64 (= 1 × 64)

[C] The tone most easily reproduced by the vocal cords of a man.
[B] The tone most easily reproduced by the vocal cords of a woman.
[A] The tone which the telephone receiver responds to most readily.

The table covers the range of the human voice, male and female.

All the intermediate tones, with their sharps and their flats, are produced
each by its own separate dynamo.
The insignificant amount of current required to operate a telephone receiver
makes it possible to furnish the music of these dynamos to many and far
distant telephones. This naturally suggests the idea of having a great
musician perform upon the keyboard and have many auditors scattered
about the city in their private homes or even in many public halls, for the
telephone receiver can readily be made audible to a good-sized audience.

XVIII

ELECTRIC BELL OUTFIT FOR THE
COTTAGE
he boys asked me what arrangement of electric bells we needed at the

T cottage and so I gave them this problem to work out by themselves:
1. We want a bell in the kitchen to be rung by a push button at the front
door. But there are times when no one is in the kitchen and hence,
2. We want a bell upstairs to make a single stroke whenever the kitchen bell
is rung from the front door.
3. We want a floor push under the dining-room table which will cause the
kitchen bell to ring a single stroke.
4. We want a push button in the dining-room which will cause both bells to
clatter and call people from their beds, from the piazza, the lawn, etc., to
their meals.
This equipment needs only one battery of two dry cells, two bells, three
push buttons and about two hundred feet of wire. It should cost less than
five dollars.
The boys drew many plans and tried many schemes and at last determined
upon the plan shown in Fig. 173.
P is the floor push under the dining-room table. When the circuit is closed
at this point the current leaves the battery from the carbon pole c, passes up
and around the magnets of the kitchen bell and back to the zinc pole of the
battery z by way of the push button P. All other circuits are open.
P´ is the push button at the front door. When the circuit is closed at this
point the current leaves the battery at c, passes up to the right-hand binding
post of the kitchen bell and divides, part going through each bell. The
portion of the current which goes through the kitchen bell passes around the

magnets and through the armature to the
left-hand binding post before it can find a
path back to the battery. Hence, the kitchen
bell clatters. The portion of the current
which passes to the upper bell goes around
its magnets and finds a path back from the
middle binding post to the battery by way
of P´. Hence the bell upstairs rings with a
single stroke.
P´´ is a push button situated upon the wall
by the side of the door which leads from
the dining-room to the kitchen. When the
circuit is closed at this point, the current
leaves the battery at c, passes up to the
right-hand binding post of the kitchen bell
and divides, part of it going through each
Fig. 173 bell. The portion which goes through the
kitchen bell passes around its magnets and
through its armature to the left-hand binding post, then up to the middle
binding post of the upper bell, through its armature to its left-hand binding
post and back to the battery by way of the push button P´´. The other
portion of the current passes directly up to the right-hand binding post of
the upper bell, around its magnets, and through its armature to its left-hand
binding post, thence back to the battery by way of the push button P´´.
Hence, both bells clatter and keep time with each other. The upper bell will
ring independently of the lower bell, but the lower bell is dependent upon
the upper one to open and close its circuit, somewhat as a relay.
Soon after the cottage had been equipped with electric bells I went to the
mill one day and found a push button at the door. Upon going in I was
curious to examine the electric bell outfit of that place and found what is
illustrated in Fig. 174.
A switch, S, had been attached to the bell. The boys said that when they felt
well they kept the switch upon the left-hand point and the bell rang as a
clatter bell. When they felt a little sick they put the switch upon the middle
point and the bell rang with a single stroke, but when they felt very sick
they put the switch upon the dead point and the bell did not ring at all.

Fig. 174

XIX

USING ELECTRICITY TO AID THE MEMORY
or the sparking equipment of the motor boat we use dry cells which

F have an internal resistance of not more than .06 ohm. They will, when
short circuited through the ammeter for only an instant, give 25
amperes.
(1.5 volt)/(.06 ohm) = 25 amperes
When we allow for a slight resistance in the ammeter itself, and for the drop
in voltage, we see that the internal resistance of a cell must be even less
than .06 ohm.
After being used about two months upon the motor boat these cells develop
more internal resistance, and they will then show not more than six to ten
amperes when short circuited through an ammeter. They are then not
reliable for ignition of the engine, but are quite as good as ever for bell-
ringing, and often continue so for more than a year. The result is that we
always have more partly run-down dry cells than we can use. Seeing them
about has stimulated the boys to devise ways for using them.
The housekeeper is distracted by carrying on so many cooking processes at
one time. She forgets the eggs, and lets them boil five minutes instead of
three because the coffee must percolate twelve minutes, and she lets the
coffee percolate twenty instead of twelve minutes because the biscuit must
bake twenty minutes, and the biscuit are forgotten because the pies must
come out in thirty minutes, and the cake in forty minutes. All this worries
the cook. Harold is a sympathetic boy and enters into the troubles of others.
I had at one time shown him how to bore a hole in a glass plate in five or
ten minutes by using a round file wet with water. One day he presented the
kitchen with a clock, intended to relieve the burdened memory of the cook.
This is represented in Fig. 175.

An ordinary kitchen clock had a hole
bored through the glass which covers its
face. This glass is easily moved around in
its metal rim, bringing the hole over any
desired minute upon the face. One wire of
the battery is attached to a leg of the clock,
the other goes to a bell, and then the wire
from the bell is poked through this hole.
When the minute hand reaches that point
Fig. 175
the electric current is closed through the
metal of the clock, and the bell rings
warning that the eggs, coffee or what not are done.
We each urged that our memories should share in the vacation, and applied
for one of these outfits. I took one of the clocks and cut back the minute
hand so as to make it shorter than the hour hand, and then had the hole in
the glass made so that the hour hand should close the electric circuit. This
was kept at my study table and reminded me of my appointments. Some
used these clocks to alarm themselves in the morning when they slept
overtime.
Another reminder is shown in Fig. 176. C is a float which rises and falls
with the water in our house tank. A cord running over two pulleys connects
this with a weight, d, hanging in front of a scale upon the wall of the
kitchen. This indicates how much water there is at any time in the tank,
which is situated in the garret. The boys arranged a bell and battery so that
when the tank is nearly empty the weight d will pull upward a spring, a, and
make it close the circuit through the bell to warn that water must be
pumped. When the tank is nearly full the weight d pushes down the spring b
and rings the bell again.
Harold said that yeast cakes were the heaviest tax upon our memories. If
some one started for the village store, before he got out of hearing, a call
would come after him, "I forgot the yeast cake. Please put that on the list."
When one returned from the village store with numerous packages, he
would generally hear, "My yeast cake was forgotten." We tried all sorts of
schemes to get rid of this yeast-cake nuisance, and finally adopted Harold's
"curled bread" project.

We had built a brick oven out back of the
house for experimental purposes. Harold
proposed that the boys bake a month's
supply of bread at a time, and, when it was
a day or two old, cut it all into thin slices
and let it dry. These slices curled up as
they dried and were known as "curled
bread." A flour barrel was filled with it
each month. It kept perfectly any length of
time. The family voted it to be better than
crackers and better than fresh breadstuff of
any kind.
Harold's suggestion regarding yeast cakes
worked so well and was such a relief to
our memories that I proposed he next
attack the problem of the often forgotten
salt in cooking.
Fig. 176

XX

THE ELECTRIC BRICK OVEN
e had no end of experiments with brick ovens. One of the most

W interesting was that wherein we used the brick fireplace as an oven
and did the family baking in it. On a cold morning we would build up
a smart wood fire in the fireplace and enjoy it during breakfast time. Then
we shovelled out the coals and the ashes, and shut it up tight with a sheet
iron arrangement and utilized the heat stored in the bricks for doing all sorts
of cooking.
Our outdoor brick oven and our monthly baking day were such a success
that they led to the construction of another oven of smaller dimensions for
the kitchen. This one was heated by electric lamps—one in each of the eight
corners. It had double glass doors in front so that the cooking process might
be watched. The glass of the inner door would be clouded with moisture for
a while, when the cooking first began, but this would soon clear up, and
then the lamps enabled us to watch the colour changes in baking, etc. The
lamps in the upper part of the oven were connected with a different switch
from those in the lower part of the oven, so that we were able to control the
browning on top or bottom at pleasure.
Harold introduced a device for automatically controlling the temperature of
this oven.

Fig. 177

Strips of brass and iron, B and I (Fig. 177), were riveted together. These
were fastened in the socket A. They are shown edgewise in the diagram.
The upper end of this compound strip is free to bend back and forth in the
plane of the paper, as here represented. They normally touch the screw C.
One of the electric light wires runs from the lamps in the oven to this screw
C. One wire of the dynamo circuit G goes to the lamps, and the other
connects with A. Thus the compound strip acts as a switch to open and close
the circuit upon the lamps.
This thermostat, as it is called, was placed inside of the oven. Heat causes
brass to expand more than iron and therefore when the temperature reaches
a certain height the thermostat curves, so as to break the contact with C, and
the lamps go out. When the temperature falls a little the thermostat
straightens until contact is again made with C. C is a screw and can be
made to advance or recede in its socket E, so that the temperature of the
oven may be maintained at any point desired. The wire of the screw C
extends to the outside of the oven, where it carries an index, D, over the
face of a dial, as shown in Fig. 178.
The cook may set this index at any desired degree, and the lamps will
indicate when that degree has been reached. The thing to be baked is then
put inside and the clock, illustrated in Fig. 175, is set so as to warn when the
time is up.

The electric spark which occurs when the
thermostat breaks contact with C causes
the metals to corrode at that point, and
corroded metals are poor conductors. This
corrosion is due to the oxygen of the air.
There is one metal—the expensive
platinum—which is not corroded by the
electric spark. We drilled small holes in the
end of the screw C and in the brass strip
and pounded into these holes little pieces
of platinum wire. Harold said he felt like a
dentist filling a tooth. This furnished good,
clean contact at all times. Fig. 178
It takes a long time to heat up the brick
oven, but it holds its heat a long time and makes an excellent fireless cooker
after the lamps are turned out. It does not allow heat to escape into the
kitchen, which makes it a comfort in our summer cottage. We are all
becoming daft on slowly cooked food—a sort of ripening process which
gives time for the chemical changes to take place and develops the finest
flavours of the food.

XXI

ELECTRIC WAVES
uch has been said about bringing young people up to do what they

M don't like to do so as to make them strong and virtuous. My own life
has always been guided by a different principle. It is: Find something
worth while which you will enjoy doing, and do it with your might. I am
bringing up my boy on the same principle. In September we have a real
desire to get back to our work in the city, and in June we have an eager
longing for the occupations of Millville. I am not aware that there is any
part of my work which I would like to be relieved from, and Harold and his
mother said that they were now ready to return to the city apartment with
real pleasure for a winter.
One evening we were seated about the dinner table when Harold asked me
how electricity could travel without wires. I replied, "It travels as light does.
But I am very much puzzled to know why it ever follows a wire when light
does not." This did not settle the question and left us both unsatisfied, so I
told him to invite two or three of his best friends in to-morrow evening, and
I would perform some experiments for them that would at least help them to
think further upon this subject.
When the evening came I showed the boys an automobile spark coil to
which I had attached two knobs, a and b (Fig. 179), and with which I had
connected two dry battery cells. When I touch the wire c to the binding post
d a spark passes between the knobs a and b. When this spark occurs at least
four kinds of waves pass out in all directions from the spark gap between
the knobs.

Fig. 179

First, sound waves go through the air. Our ears detect these. If the air is
removed from around the apparatus no sound wave can go forth. A careful
examination of the internal ear shows us that it is constructed so as to
respond to such air waves.
Second, light waves go forth. These affect our eyes. We are blind to the first
kind of waves and deaf to the second. The light waves travel without air—
somewhat better without air than with air. A microscopic examination of the
eye indicates that it is constructed so as to respond to waves. We believe
there are waves in the ether which fills all space. Sound waves travel in air
at the rate of one mile in five seconds. We had this nicely illustrated at the
sea shore one summer. The steamer touched each morning at a wharf which
we could plainly see two miles distant. We could see the steam arise when
she blew the warning whistle, and with our watches we found that it always
required ten seconds for the sound to reach us after we saw the steam of the
whistle. This at least showed us that it takes five seconds longer for sound
waves to travel a mile than it does for light waves to travel the same
distance. For light had to travel the same distance before we could see the
steam arise from the whistle. Although the time it takes for light to travel a
mile is inconceivably small, we have a simple method of finding out that it
requires eight minutes for light waves to come to us from the sun.
The satellites of the planet Jupiter, in revolving about that body, disappear
and reappear at regular intervals, acting as flash lights to mark time.

The earth, being 92,000,000 miles distant
from the sun, is 184,000,000 miles farther
from Jupiter when at B than it is when at
A. (See Fig. 180.) It is found by
observation that sixteen minutes more are
required for the light waves from a
reappearing satellite to reach us at B than
when we are at A. Hence eight minutes
would be required for light waves to travel
the distance from the sun to the earth.
Although light travels at the inconceivable
velocity of 186,000 miles per second, the
nearest star is so far distant that it takes
light three and a half years to come from it
to us. The North star requires forty-two
years to send its light to us, and Arcturus is
so far away that waves of light sent out
from it one hundred and sixty years ago
are only just reaching us now, and if it
should cease to send forth light now men
would continue to see it for five
generations yet to come.
A third kind of wave which goes forth in
the ether from the spark gap of our coil is a
heat wave. This affects neither our eyes
nor our ears, but I will undertake to make
Fig. 180 you conscious of it by another method.
Before a
mixture of gasolene vapour and air can be
ignited its temperature must be raised to
about 2000 degrees Fahrenheit. I will show
that heat waves pass out from this spark
gap by placing my watch crystal filled
with gasolene underneath the knobs of the Fig. 181
spark coil, (Fig. 181). When now I close
the electric circuit at the battery the

mixture of gasolene vapour and air just above the watch crystal is ignited. If
I increase the distance between the knobs you still hear the crackle of the
sound waves and see the light waves, but the mixture of gasolene vapour
and air does not ignite, because there are not heat waves enough. The
automobilist expresses this fact by saying a "fat" spark or a "warm" spark is
needed. A battery which has ceased to give a sufficiently hot spark to
explode the mixture of gasolene and air in the cylinder of a gasolene engine
may serve all other purposes quite as well as ever. It may ring bells almost
as long as it ever would.
I proved that the temperature for igniting a mixture of gasolene vapour and
air was nearly as high as melting iron, by heating an iron rod to a dull red
heat and bringing it to the watch crystal containing gasolene. It did not take
fire. I showed that it could not be ignited by a lighted cigar, nor even by a
glowing coal taken from the fire.
It was necessary to heat the iron rod to a very bright red heat—nearly white
heat, or nearly to its melting point, before it would ignite the mixture.
These heat waves are ether waves, differing from light only in having
greater wave length. They travel at the speed of light, they travel better
without air than with air. They come from the sun and all other light-giving
bodies. Indeed, an ordinary incandescent electric lamp gives out about
twenty-four times as much energy in heat as in light. Heat waves are being
thrown off from all bodies which are around us. The steam radiators are
placed in this room for the express purpose of sending out heat waves
through the ether in this room. This is the chief method of distributing heat,
and it is hindered rather than helped by the presence of the air. The walls,
ceiling, floor, furniture, people—everything here is sending out heat waves.
The fourth kinds of waves, which go out from the spark gap of our coil, are
also waves in the ether. They are still longer than heat or light. We have ears
for sound, eyes for light, and temperature sensation for heat, but as yet we
have not evolved a delicate sense organ for detecting electric waves. At
least few of us claim to have such a sense. I will, however, undertake to
make you feel electricity. I then adjusted the coil so that each boy might
take a mild electric shock from it by touching the two knobs. That is by
placing himself in the spark gap. They agreed that although they could not

hear, see, taste, or smell electricity they were a little more familiar with it
now, having felt it.
Sound waves in air, as given out by the piano, vary in length from, say, four
inches to forty feet, those having the shorter wave length being the higher
pitched tones.
Light waves in the ether, as given out by the sun, vary in length from, say,
1
⁄60000 to 1⁄80000 of an inch, those having the shorter wave length being the
violet-coloured light, which may be seen in the rainbow, and those having
the longer wave length being the red-coloured light of the rainbow or the
sunset.
Heat waves, which are also waves in the ether, vary in length from above
1
⁄80000 to, say, 1⁄5000 of an inch. Roentgen or X waves are ether waves,
shorter than light; while Hertzian, or wireless telegraph waves are very long
ether waves, varying from a few feet to many rods in length. Those used by
Marconi in sending despatches across the Atlantic Ocean are as long as
1000 feet, four or five of them cover a mile, and 12,000 of them cover the
whole distance from Cape Cod to Poldhu.
Electric waves are easily broken up into the shorter heat waves, or the still
shorter light waves. On the other hand Roentgen waves are readily
transformed into the longer light waves, and are thus brought within our
powers of vision.
Sound waves of various lengths (of high and low pitch) all travel at the
same speed (one mile in five seconds), else how would the piccolo and the
bass horn of the distant band sound together. So ether waves of various
lengths (light, heat, electricity, etc.) all travel at the same speed, i. e.,
186,000 miles per second.
For detecting the electric waves which may be sent out from the spark gap
of our automobile spark coil I shall ask you to help me prepare a special
piece of apparatus. One boy may file this silver ten-cent piece and another
may file this nickel five-cent piece, each gathering the filings upon a piece
of paper. A third boy may select a piece of glass tubing about one eighth of
an inch in the inside diameter, and with a three-cornered file cut off a short
piece, about one and a half inches long, and smooth the ends with a wet file.
A fourth boy may select a piece of stout copper wire nearly as large as the

bore of the glass tubing, and cut from it two pieces, each about two inches
long. Wind one end of each of these with thread to make them fit snugly in
the glass tubing.

Fig. 182 Coherer

We thrust one of the wires into the tube, then mixed equal parts of the silver
and nickel filings and put as much of the mixture into the tube as we could
hold upon the tip of a penknife blade, and then thrust in the other copper
wire. (See Fig. 182.) The ends of the wire were about one eighth of an inch
apart and the gap was loosely filled with the metal filings. This was
connected by short pieces of copper wire, as shown in Fig. 183, to a dry
battery cell, B, and a sensitive ammeter. When all connections were made
the needle of the ammeter remained at zero, showing that no electric current
was passing, that is, the battery cell was unable to send any electricity
through the metal filings.
This is the apparatus which is to help us detect electric waves when they
pass about us. Electricity has been called invisible light, that is, invisible to
our eyes, and this apparatus has been called an "electric eye" because it will
detect electric waves in the ether, just as our eyes may detect light waves
passing through the ether.
We placed the automobile spark coil upon the table near to the tube
containing the filings of silver and nickel, and as soon as we made a spark
pass between the knobs the ammeter needle moved half way across the
scale, indicating that the spark had somehow influenced the metal filings in
the tube so that now they permitted the battery cell to send some electric
current through them and through the ammeter. I asked one of the boys to
tap the tube slightly with a lead pencil so as to jar the metal filings, and as
soon as he did so the needle of the ammeter went back to zero.
The spark coil sent electric waves out in every direction, and those which
hit the metal filings made them cohere together. In that condition they

allowed
the dry
cell to
send
through
them
enough
current to
move the
needle of
the
Fig. 184
ammeter.
Tapping
Fig. 183
the tube made the metal filings break apart
again, in which condition they do not
allow the current of the cell to pass in sufficient quantity to move the
needle. This tube is called a coherer, because the filings in it cohere
together. The apparatus then serves to indicate when electric waves are
passing. As yet, however, it would not respond when the spark coil was
more than one foot away. Our next step was to attach extra pieces of wire,
each ten or twelve feet long, at either end of the coherer, as indicated in Fig.
184. One of these wires was stretched out upon the floor while the other one
was connected with the wire of a picture hanging upon the wall.
We now found that the coherer would respond when the spark coil was
operated several feet away. The extra wires which we had attached to the
coherer are called antennæ, because they suggest the long "feelers" or
antennæ of some insects.

Fig. 185

Our next step was to put antennæ upon the
spark coil also, as shown in Fig. 185. One
of these wires was stretched out upon the
floor, while the other one was connected
with the wire of a picture hanging upon the
wall on the opposite side of the room from
where the coherer was. We now found that
the coherer would respond when the spark
coil was operated in the farthest part of the
room. With the wires which were lying
upon the floor extending toward each
Fig. 186
other, but lacking several feet of touching,
the coherer responded when the spark coil
was operated in various other rooms of the house, although the doors
between were shut. When the floor wires were connected to the water pipes
the coherer would respond when the spark coil was operated in a
neighbouring house. We tried a similar experiment, substituting an ordinary

electric bell for the spark coil. The coherer or electric eye detected that ether
waves were sent forth from an electric bell every time a spark was produced
in the bell. For this purpose connections were made, as shown in Fig. 186.
One dry battery cell was used to ring the bell. The floor wire a, or, as it is
usually called, the ground wire, was connected to the binding post 1, and
the other antenna was connected to the screw 3, and then supported aloft on
a picture hung upon the wall. With this transmitter we sent waves across the
room which were detected by the coherer.
We constructed a simple spark coil as
follows: We bought a pound of No. 24
single cotton covered copper wire, such as
is used in the electro-magnets of bells. It
was, when we bought it, wound upon a
wooden spool. We filled the hole in the
centre of this spool with wire nails. One
dry cell was connected with this (Fig.
187). When the wires at d were touched
together, and then separated, a spark was
produced at that point. A ground wire was
connected at b, and an antenna at c, as
Fig. 187
before. Using this apparatus now as a
transmitter of ether waves, we found that
the coherer detected them.
We next gave our attention to making
changes in the receiving apparatus, not to
change the coherer, but to provide
substitutes for the ammeter. A sensitive
relay was procured, which is essentially
like a bell or buzzer except that it does not
clatter. It will be readily understood, by
referring to the accompanying Fig. 188,
that R is a coil of insulated wire around an Fig. 188
iron core exactly like what we see in the
electric bell. (In practice there will be a
pair instead of one of them.) Such coils are called electro-magnets, because
when electricity flows in the wires they become magnets, and will attract

iron. A is an iron spring, B is a dry battery cell and C is the coherer.
Whenever an ether wave passes the coherer permits the battery cell to send
a current around the magnet of the relay, and it attracts the iron spring a, so
that it hits against the metal post d with a click. Whenever we used this to
respond to ether waves the click of the relay suggested the telegraph
sounder. How it served in wireless telegraphy will appear in the following
pages.

XXII

RINGING BELLS AND LIGHTING LAMPS BY
ELECTRIC WAVES

Fig. 189

arold was to have a birthday party, to which many of his school

H friends were invited. For this occasion he prepared, with my help, to
perform for the girls and boys some electrical experiments, and
particularly to give all who chose to try it an electric shock. For this purpose
he had them all join hands, and the electric charge was sent through the
whole line at once. One thing he did shocked his mother more than
anything else. He instituted a mock court, at which one of the boys was
tried, convicted and condemned to be executed by electricity. The whole
affair was enacted with no great solemnity, but the electrical experiment
was voted a great success by the executed "criminal." The following group
of experiments, however, seemed to give the most satisfaction: On a table
was placed the coherer connected to the relay, and in another room was
placed the spark coil for sending ether waves. He had this operated by a
confederate whom he chose for the purpose. He then connected two wires
to the relay, one at d and the other at e (Fig. 189). These ran to a battery cell
and a bell in a far corner of the room. At a given signal (a cough) the
confederate made a spark at the spark coil in the other room; this sent ether

waves through the partition between the rooms; the ether waves caused the
coherer to pass electricity from the dry cell No. 1, to close the relay spring
R. This acted like a switch to close the second circuit through the dry cell
No. 2 and the bell, which rang out to the surprise of all. It continued to ring
until he tapped the coherer tube and broke apart the filings. When this had
been tried to the satisfaction of all, the company was invited to another
room. Here they found an electric train with tracks, train sheds, stations,
tunnels, bridges, switches, signals, etc., arranged upon a centre table. The
electric train was to be started by ether waves. A wire from the railroad
track was connected with e of the relay (See Fig. 190). A wire from d of the
relay was connected to the third rail through a battery of sufficient strength
(Battery 2). The electric train completed the circuit by connecting the tracks
with the third rail. All heard the crack of the spark coil in the adjoining
room, and saw the train start immediately. Ether waves had caused battery 1
to close the relay R. This had closed the circuit so that battery 2 might run
the train, of course by means of a motor in the train. He tapped the coherer.
The relay spring R flew open and the train stopped. Presently another crack
from the adjoining room, and the train instantly started again. When all the
details of the electric train had been examined the company was invited to
go to the dining room, which was dimly lighted by candles. All were seated
and busily conversing when the crackling noise of the spark coil was again
heard, and a group of little electric lights flashed forth upon a birthday cake.
The wires from the lamps and a battery to run them had been connected
with the binding posts d and e of the relay.

Fig. 190

The chandelier over the dining-room table had a pendant push button A
(Fig. 191), with which the regular electric lights could be turned on and off.
This I had removed and extended the wires down upon the table. It was

only necessary to connect these to the
binding posts d and e of the relay, and the
next wave from the spark coil lighted the
chandelier.
The flexible wires underneath the dining-
room table with which the maid is usually
summoned from the kitchen were next
extended up and connected with d and e of
the relay, and the maid was called in by an
ether wave. She brought with her a tray in
the centre of which stood an earthenware
cup, such as is used for baking custard. Fig. 191
This had been filled with a mixture of
granulated sugar and powdered potassium chlorate. Four dry battery cells
stood around this upon the tray connected in series (Fig. 192). A very small
iron wire connecting two of these cells dipped into the sugar mixture. Two
wires from the battery were connected to d and e of the relay. At the proper
signal an ether wave was sent out by the spark coil. The coherer closed the
relay and the relay acted as a push button to close the circuit of the four
cells upon the tray. The fine wire dipping into the sugar and potassium
chlorate got red hot. This caused the mixture to flash up and burn in most
beautiful coloured flames. (Fig. 193).
On this occasion Harold's
friends gave him, with due
formalities, the degree of E.
E., which they said meant
electrical expert, and ever
since that night he has been
called "the expert." I
inquired of the young folks,
as their party was breaking
up, if they understood
Harold's explanations of all
Fig. 192
these things, and he replied
that he at any rate Fig. 193
understood them better having attempted to explain them.

XXIII

TELEGRAPHING BY ELECTRIC WAVES
he next time Harold and I
T experimented we arranged something
to save us the trouble of tapping the
coherer each time we used it. We
employed simply an electric bell, B (Fig.
194), from which we removed the gong.
By reference to the figure the arrangement
will be understood. Each time ether waves
cause the metal filings to cohere and the Fig. 194
1
battery B closes the relay R, battery B 2

causes the hammer of B3 to tap against the coherer. This causes the current
to cease to flow from B1 and the relay opens again by its own spring.

Fig. 195

Our next addition was a telegraph sounder as shown in Fig. 195. B1 is a
single dry cell, C is the coherer, R is the relay, B2 is now a battery of three
cells. Part of its current goes to B3, the tapper for the coherer, and part of its
current goes to the electro-magnet of the telegraph sounder S. Ordinarily a
spring holds the iron strip d up against the metal stop a, but when the
current passes through the electro-magnet it pulls down this iron strip with a
click against the metal stop e. But while this is happening C is being tapped
by B, and is ready to respond to each wave. It was only necessary now to
have some code of signals in order to communicate by telegrams. We
learned the system of dots and dashes, or short and long periods marked off
by the sounder, which all telegraphers use and which is known as the Morse
alphabet, and very soon Harold and I were telegraphing from one room to
another messages of several sentences at a time, the Morse alphabet being
told off on the spark coil and being received through the coherer and
telegraph sounder. It was not long before Harold and one of the neighbours'
boys were exchanging messages between their homes, each having a spark
coil and the necessary receiving apparatus, and having extended their
antennæ to the top of the buildings into what are called in the wireless
language aerials.

Photograph by Helen W. Cooke
Induction Coil of a Wireless

The fever for wireless telegraphy spread like wild-fire among the boys. In a
few months they had formed a "wireless club." They had each read
anywhere from ten to thirty books and articles upon the subject, and had
secured the latest improved apparatus. They made it a practice to spend
hours daily at their instruments picking up and keeping on file messages
which were sent to and from steamers leaving the harbour for European
ports. On one occasion they showed me from these files scores of messages

—fond, personal, and supposedly private farewells to friends and
communications between business partners which they would never have
made on land without first closing the office door. The boys had acquired a
mass of technical knowledge upon the subject which far exceeded my
comprehension. But their teachers in school complained that they would
learn nothing else, and some of the boys had already received warning that
they might fail of promotion.
How to have compelling interests without riding hobbies is the great
problem for both boys and men. I have known many boys who could, or at
least would, do nothing well in school or out, except some specialty like
manual training or science. In later years they were so deficient in education
that they could hold no worthy position in anything. My anxiety was to save
my boy from such a fate. I was determined that he should have a fair share
of all kinds of culture. To this end we read together much of biography,
history and classical literature, ancient and modern, through the medium of
the English language.
As both prevention and cure of the wireless telegraph mania I deemed it not
necessary to suppress enthusiasm, nor to introduce obviously useless tasks
for the sake of the training which might be in them. My method was, on the
contrary, to encourage my boy to have several hobbies which he might ride
with enthusiasm, but to make it a rigorous rule to exchange his "mount"
occasionally.

XXIV

HALLEY'S COMET AND ELECTRICAL
WAVES

Fig. 196

t was the year 1910 and Halley's comet was approaching the sun. On

I May 18 its tail might be expected to reach the earth. Astronomers had
requested all who might be possessed of wireless telegraph apparatus to
watch on that day for any peculiar behaviour of their apparatus so that
evidence might be obtained whether or not the comet sends forth such ether
waves as we call electricity. Harold desired me to explain the whole matter
to his group of friends, which I did on a subsequent evening, as follows:
"Although Halley's comet has come within the earth's orbit about three
thousand times since its first recorded appearance, I know of no man living
who can give a satisfactory account of having seen it. Any one who has
seen it before must be at least seventy-five years old, for it requires seventy-

five years to make one complete circuit of its own orbit. But no one who is
now seventy-five could have observed it intelligently, and even one who is
now eighty-five years old would have to tell what he saw when he was ten
years old and has remembered for seventy-five years. Furthermore, any
account of how it looked on a former return is no guide to how it may
appear on this trip. You may properly think of the comet as a group of solid
pieces no bigger than the stones you may throw, scattered, two or three to
the mile, through a space 12,500 miles broad. This extremely thin cloud of
particles does not reflect enough sunlight to be visible, even in a telescope,
in any part of its journey, and hence we should be wholly unaware of its
existence if it did not sometimes have the strange faculty of giving out light
of its own while in that part of its own orbit nearest to the sun. At such a
time there is a hazy light enveloping the mass of small bodies, and
streaming away sometimes many million miles from them. The mass of
small bodies is generally referred to as the nucleus, and the stream of
luminous gas which the nucleus gives forth is called the tail, though it
reminds me more of a search-light.
"It does not trail along behind the comet but always points away from the
sun (Fig. 197). The normal thing for a comet to do is to begin to develop a
faint light and a short streamer as it gets near to the sun, to have its light
grow brighter and its streamer to grow longer until it reaches the point
nearest the sun, and then to have its light grow dimmer and the streamer
grow shorter as it recedes from the sun.
"It has many times been suggested that this strange search-light appearance
may be an electrical phenomenon, some form of ether waves which the
comet sends forth when under the immediate influence of the sun. But not
all comets are alike in this matter, nor does the same comet always act alike
on succeeding trips, so that we may not predict what Halley's comet will do
on this visit. It would be natural to suppose that Halley's comet, like radium,
might in time lose the power to radiate off material, in which case it might
at length become wholly invisible to us, even though it continued to travel
in its wonted path. Our only way of knowing of its existence then would be
that on its returns some of its small pieces might be attracted to the earth
and enter our atmosphere as meteors. This sort of thing is continually
happening, and may be the last reminders of once brilliant comets.

"For almost a century it has been the common
belief that light is merely a wave motion in the
ether. Our eyes respond to ether waves of certain
length only. Waves a little longer than those
which affect our eyes are felt by us as heat
waves. Waves still longer than those of heat are
the so-called electric waves. These we use in
wireless telegraphy. There are still shorter waves
than those of light. These affect the sensitive
plate in photography. They help to form the
green material in the leaves of plants and the
brilliant colours in flowers. They assist in the
fading of our clothes and the tanning of our
skin. These are called chemical waves. Still
shorter waves in the ether than those of which
we have just spoken are the X rays, and all the
strange things which they may do have not yet Fig. 197
been determined. Certain it is that they can
make dreadful sores in our flesh. They can penetrate through wood and
paper, but not metals. They pass readily through flesh, but not bones. All
such ether waves are treated in a book by Sylvanus P. Thompson, entitled
'Light Visible and Invisible,' in which he points out that electricity, heat,
light, chemical rays, etc., are all alike in being ether waves, and this was
suspected by James Clerk Maxwell and others half a century ago, and has
come now to be quite generally believed.
"Halley's comet, already having been seen upon this return, must be sending
out those ether waves which we call light; whether it is also sending forth
some of the other kinds of ether waves may yet be determined."
My audience being chiefly composed of those persons who were present at
Harold's birthday party, they pressed me to tell them more about wireless
telegraphy and similar matters, and so I agreed to give them at some future
date some account of the history of these ideas. But my present purpose was
to start an interest in astronomy as an antidote for the wireless epidemic,
and so I invited all who desired to do so to come again one week from that
evening, bringing with them such opera and field glasses as they might be
able to secure. I promised to show them how to make a telescope such as

Galileo had more than three hundred years ago. I agreed to go out with
them several evenings and scan the sky with our telescopes, and to tell them
of some readable books and articles upon astronomical matters.

XXV

HOW THE IDEA OF A UNIVERSAL ETHER
DEVELOPED
he evening for the meeting of the Science Club had arrived. Its
T membership had increased tenfold within a year. At its monthly
meetings, which were open to the public, an audience of two hundred,
old and young, was usually present—a number about three times that of the
regular membership. General science was now the study of this club. At its
weekly meetings, which only members attended, the studies of specific
topics by individuals, oftentimes illustrated by experiments, were reported.
These meetings were held in one of my laboratories, while the open
monthly meeting was always held in my lecture room, with some rather
famous speakers to instruct the audience. An enthusiastic friend of science
had given a fund with the stipulation that we should engage the services of
those who both knew their subjects and had acquired the art of presentation.
The fund was $10,000 and it yielded $500 a year. I think beyond question it
was doing more for science than any other fund of ten times that amount
which can be mentioned.
On the particular evening of which I am about to speak, the lecturer told the
members of the Science Club frankly how, beginning at the age of thirteen,
he had spent forty years of enjoyment in study, that he had always found
great satisfaction in the study of ancient civilizations and literatures. He had
been fortunate, he said, in having teachers early in life who could make
these subjects full of meaning to him. His greatest satisfaction, however,
during the last twenty-five years had been found in tracing the development
of modern science, both in the evolution of its theories and in its
applications to modern industries. He said he was sure that young people of
high-school age would find it profitable to learn, for instance, how the
modern theory of combustion had developed slowly through the centuries,
even if to do so they must curtail somewhat their study of how Greece and

Rome developed and declined. He said that science furnished a
tremendously rich field of study for young people, which as yet had been
untouched by our schools, first, because educational conservatism had made
it impossible to determine the relative importance of subjects of study, and,
second, because education in science had, for a brief period, found its worst
enemies within its own camp. He would like especially to commend on this
evening some historical studies in science, and had chosen for his subject,
"How the Idea of a Universal Ether Developed."
Men seem to talk freely now about the transmission of light, heat, and
electricity by means of the ether. How did this idea arise? Is it a product of
wild imagination? or did the idea develop out of experiences which, if given
to any person of fair intelligence, would yield the same result?
A little over thirty years ago, at the Royal Institution of Great Britain, James
Clerk Maxwell (1831–1879) delivered a lecture on "Action at a Distance."
It was no new subject, but rather one of the oldest and most often discussed
subjects from the days of the ancient Greeks down to the present. We talk of
gravitation as an attraction or pull between the various bodies of the
universe, but how can they pull one another without some material bond
between? This was Sir Isaac Newton's great puzzle which he never solved,
though he expended upon it the greatest efforts of his great intellect.
The sun appears to repel the tail of the comet, yet how can there be a push
without intervening material with which to push? When we speak of light
pouring or streaming in, do we think of it as a substance? When we speak of
warm bodies losing heat, or when we cover them to keep the heat in, are we
thinking of heat as a substance? What are heat, light, electricity, magnetism,
and gravitation?
These are no new questions. They are certainly older than history. Various
ideas have prevailed at different times. It is much easier to change our ideas
than to change our language. You occasionally see and hear the words
calorie and caloric used in connection with heat. They stand for an idea,
abandoned for three generations, that heat is a substance called caloric,
which saturates warm bodies and drains out of them when they cool off. I
hardly think these ideas either arise or fall without good and sufficient
reason. Each theory has been the natural conclusion from our observations
of nature as far as we have gone with them. To be sure, it is difficult for us

to see how men acquired, from any observations of nature, the idea of light
which seems to have prevailed previous to the time of Aristotle, three and a
half centuries B.C. This idea was that objects were made visible by
something projected from the eye itself. Still, the questions which I have
indicated regarding heat, light, and electricity have impelled men for many
centuries to observe nature for hints as to the answers. The doctrine of the
universal ether as a medium for transmitting wave motions, and of light,
heat, and electricity as being motions of different wave length, is the natural
conclusion of the present time. It may give place to another theory when we
have further facts to reason upon. Imagine your never having seen a harp or
other musical instrument. Would it require a long time, do you think, for
you to find out its use, at least to this extent, that it will produce tones
whenever the strings are made to vibrate? That the short strings vibrate
more rapidly than the long ones, and at the same time produce tones of a
higher pitch? Imagine that having become familiar with the harp you should
successively come upon scores of other musical instruments of very
differing types. You would soon become adept at divining their uses. Now, a
study of the microscopic structure of the eye, for one thing, would suggest
that light may be in the nature of a vibration. Scores of other lines of study
in a similar manner have at length brought all who pursue them to the
conclusion that light is a form of vibration.
Robert Hooke in England (1631–1703) and Christian Huygens in Holland
(1629–1695), back in the seventeenth century seem to have been the first to
give expression to this idea, which was nothing more than an inkling in
Hooke's mind, but which was the necessary result of observations on the
part of Huygens. For nearly a century the idea lay dormant, largely because
Sir Isaac Newton (1642–1727), the cleverest thinker of his time, opposed it.
It was perhaps unfortunate for the success of the theory that Huygens, its
founder, adopted the word ether, for that was an old term, and had been
very badly overworked. The word ether, or æther as it was often written,
had been invented in the days of ignorance, for such foolish reasons as: (a)
because "nature abhors a vacuum," or (b) "for planets to swim in," or (c) "to
constitute electric atmospheres and magnetic effluvia," or (d) "to convey
sensations from one part of our bodies to another."
"When we remember," says Maxwell, "the mischievous influence on
science which hypotheses about æthers used formerly to exercise, we can

appreciate the horror of æthers which sober-minded men had during the
eighteenth century."
Newton in England (1642–1727) and Laplace in France (1749–1827)
stoutly opposed the undulatory theory of Huygens and championed a
corpuscular or emission theory, that light-giving and heat-giving bodies
emit a subtile fluid.
There is no other instance in the whole history of modern physics in which
truth was so long kept down by authority. Fresnel (1788–1827) and Arago
(1786–1853) in France appear to be the only persons during the eighteenth
century who caught a clear vision of the truth of the undulatory theory.
But it remained for Mr. Thomas Young (1773–1829), a colleague of Sir
Humphrey Davy at the Royal Institution, in his Bakerian lecture (1801) on
"Theory of Light and Colour" to bring together such good evidence for the
ether wave theory that it has hardly been questioned since.
Young, like Davy, was a most remarkable man in literature and in science.
It was he who first deciphered the Rosetta Stone, now in the British
Museum, and gave us a key to the Egyptian hieroglyphics. Probably he was
the only man who was able to overthrow the influence of Newton's
authority even a century after Newton did his work.
Faraday's (1791–1867) chief work as director of the laboratory of the Royal
Institution, London, was a study of ether phenomena, particularly electric
and magnetic. About seventy-five years ago he became impressed with the
fact that although wires may give direction to an electric current the electric
influence is not confined to the wires, but may permeate more or less
widely the region about them.
Nearly fifty years ago Maxwell (1831–1878) professor of physics at
Cambridge University, England, conceived the idea that light is electricity
of a very short wave length.
Nearly twenty-five years ago Heinrich Hertz (1857–1894), in Germany,
proved by experiments the existence of electric waves, and measured their
length and velocity, determining their various characteristics as compared
with light.
About fifteen years ago Marconi developed a wireless telegraph apparatus,
which made it possible to use electric waves for purposes of

communication.
Thirteen years ago (1897) the first wireless telegraph company was formed.
Eleven years ago (1899) the international yacht races in New York Harbour
were reported by wireless telegraph, and bulletin boards in New York City
announced to waiting crowds the details of the race while it was in
progress. Nearly ten years ago (1901) wireless despatches were first sent
across the Atlantic Ocean. Wireless telegraphy was opened for public use in
1905, and very soon the company began to coöperate with the regular
telegraph companies. Nearly all coastwise and trans-Atlantic steamers are
now equipped with wireless telegraph outfits, and a law has passed both
houses of Congress making it obligatory on the part of steamers which
carry fifty or more passengers to have such equipment. On several disabled
steamers, notably the Republic, loss of life has been averted by the wireless
emergency call for help, to which the captains of all steamers feel obliged to
respond. If you desire to communicate with a friend who left for Europe
several days ago, you simply write him a telegram, addressing it to his ship,
and deliver it at your nearest telegraph office. Each telegraph office has a
record of the location of every ship having a wireless telegraph outfit. It
despatches your message to the wireless station along the coast which is
nearest to your friend's steamer, and from this station it is sent on the ether
to the ship. Or in some cases it may be repeated from one ship to another
along the Atlantic highway until it reaches the desired one. Thus also news
of important events on either continent is distributed daily on board ships
which are crossing the ocean. There are said to be more than 50,000
amateur wireless stations in the United States, and already Congress is
taking steps to regulate the use of the wireless telegraph in order to prevent
interference with Government and other important messages.
More than three dozen books and countless magazine articles have already
been written upon wireless or ether wave telegraphy. Hundreds have and
thousands are contributing to our knowledge of ether wave phenomena. If
the names of all who have said or done something to render stable the
foundations of this idea of a universal ether, whose undulations account for
the phenomena of heat, light, and electricity, were to be mentioned, the list
would contain nearly all the important workers in the field of physics for
the last century.

XXVI

ELECTRIC CURRENTS CANNOT BE
CONFINED TO WIRES
arold said that if electricity was so much like light that it could go

H without wires he thought light ought to be enough like electricity to be
conducted by wires on occasions. I told him that I had no hope of
being able to confine light to a wire; indeed, if the Science Club would give
me an opportunity I would show them that even when electricity follows
the general direction of a wire its influence is not confined to the wire. As a
result of this bid I received an invitation to address an open meeting of the
Science Club.
In my first experiment on that occasion I
took a one-pound spool of No. 24 cotton-
covered copper wire and crowded the hole
in the spool full of wire nails A (Fig. 198).
I disconnected the wires from an electric
drop lamp and connected them to b and c,
the ends of the wire from the spool. Our
electric lighting circuit was what is called
the alternating current. I also had a second
spool, B, precisely like the first. The wires
from this were connected to a miniature
lamp, L, such as is used at the switchboard
of a telephone exchange. We then screwed
the drop-light plug into the chandelier and
turned on the electric current. I brought
spool B with the miniature lamp near to Fig. 198
spool A, as shown in Fig. 199, and when it
was within a distance of about two inches the little lamp lighted up to full
brilliancy, thus showing that while the electric current is passing in the wire

of spool A its influence is not confined to the wire, but exhibits itself in the
region outside of the wire. To illustrate still further this fact we substituted
an electric bell in the place of the lamp L, and when the spool B was
brought near to A the bell rang. But the most striking illustration was
obtained when a telephone receiver was put in the place of L. With this held
to the ear while the spool B was brought toward A a humming sound could
be heard when B was about a foot distant from A. This sound grew rapidly
louder as B approached A, until, when the spool B rested upon the spool A,
a sound like the peal of a pipe organ was heard all over the apartment. The
tone was very nearly that of the key on the piano which is two octaves
below middle C. I unscrewed the cap on the large end of the telephone
receiver, took it off, and moved the thin iron diaphragm to one side, when it
began to dance about at great speed. It was keeping time with the dynamo,
five miles away, which generated the electric current. The dynamo changed
the direction of the electric current sixty times per second, and this made
sixty vibrations per second. The dynamo sent out ether waves which
affected the telephone receiver, although the receiver was not connected to
the dynamo by wires.
To emphasize the fact that the dynamo had lighted the lamp, rung the bell
and made the telephone receiver hum without being connected with them, I
repeated all these experiments in a different way. Spool A, connected as
before with the electric lighting circuit, was concealed beneath the table.
For spool B I substituted spool C (Fig. 199), on which the wire was wound
so as to appear like a candlestick. On the top of this was placed the
miniature electric lamp screwed into a miniature socket and connected to
the wires of the spool. This "Witches' Candle," as we called it, was sitting
unlighted upon the table when I called attention to the fact that if I moved it
to a certain spot upon the table it flashed into full light. (Of course this spot
was directly over spool A.) I moved it slowly away from that spot and its
light slowly grew dim and disappeared.
On the table was also sitting a cream pitcher in which I had placed spool B
with a buzzer attached to it. Remarking that this pitcher groaned for more
cream whenever it was empty, and thus of its own accord called the waiter,
I moved it to the spot on the table directly over spool A, when the buzzer
gave forth a sound like a husky bumble-bee shut up in a resounding bottle.
At this signal my assistant came in and took up the pitcher and placed my

silk hat upon the table, when it instantly
boomed forth a base note two octaves
below middle C of the piano. Out of the
hat I took a coil and the telephone receiver
and the mystery was solved.

Fig. 199

Fig. 200

In 1819 Hans Christian Oersted in Denmark (1777–1851) first noted that
the region about a wire carrying an electric current has an influence upon a
magnet. I will show this fact by a simple experiment. I magnetize a stout
sewing needle by drawing it from end to end across the pole of a steel
magnet, and by means of a triangular piece of paper and a fine thread I
suspend it a few inches above the table (Fig. 200). I then lay upon the table
a piece of wire parallel with the needle and fasten one end of it to one
binding post of a dry cell. Whenever I touch the other end of the wire to the
other binding post of the cell, thus sending an electric current through the
wire, the magnetized needle is deflected at right angles.
This experiment, performed by Oersted, seems to have started Faraday
upon that wonderful series of researches which has resulted in giving us the
dynamo.

XXVII

WIRELESS TELEGRAPHY IN EARNEST
e had decided to let Harold make a trip to Europe alone. The first

W message from him after his departure was a brief note to his mother
saying that they had had a turbulent voyage, but all had landed safely
upon the other side, none the worse for their experiences.
The next day a number of letters came to me from total strangers. One of
these ran as follows:
My Dear Sir:
Prompted by my own impulses, and urged to do so by the passengers under my
charge, I improve this first opportunity to express to you our high appreciation for
your noble but very modest son, to whom more than to any one else we owe the lives
of all on board our fated ship.
I am sending this direct to you both, because I understand a father's heart and because
the young man escaped as soon as we came to land, without any of us learning his
address. I beg you will communicate to him the desire of the president of our
company to meet him and personally to thank him for his gallant conduct. I am also
instructed to say that whenever Harold desires to cross the ocean the best which any
ship I may command can afford will be his without charge.
Very respectfully yours,
———— Captain.
S. S.

Another letter was the following:
My Dear Sir:
Permit me to congratulate you on having such a heroic and self-possessed son. We,
his fellow passengers, are, if possible, as proud of him as you must be.
I fear that his account of the affair will not do himself full justice, and so, with your
permission, I will give you the full details as I have gathered them from the
passengers, from the crew, and from my own observation.
During the last night of our voyage a thick fog closed about us. The constant blowing
of the fog whistle made the night dismal. Few persons slept at all. About two o'clock
in the morning the ship struck a reef, and instantly it seemed as though every person
on that ship reached the decks at the same time. The water poured in and put out the
fires. The ship heeled badly, and it seemed that any minute she might slip off the reef

on which she was resting into deep water and go down. To add to our horror fire
broke out. It seems to have started in the wireless operator's room.
Very much damage was done to the wireless outfit itself, and the operator was badly
burned, so much so that he was taken to the ship's hospital suffering with many
painful and dangerous wounds.
Meanwhile the flames spread rapidly and we were unable to summon help. The crew
and many of the passengers fought the flames, but with little success.
In the midst of our despair word passed around the ship that an unknown boy from
among the passengers was sending the C. Q. D. message to all the world by wireless.
It was afterward learned that your Harold was the youth. He had repaired the damaged
apparatus sufficiently to establish connection with a storage battery which he found,
and, under the captain's direction, was sending forth that hurry call for help known to
all the wireless fraternity and heeded by all sea-faring men. I learned that your boy
was not a regular operator, but that somehow he had learned to send this message and
also to send out the captain's calculations of our position at sea. He was also able to
detect that his call had been heard and that help was coming, although he could not
understand much that came to his instrument in reply to his calls. I learned, also, that
he was one of the first to reach the operator's room and to give assistance. He was
himself badly burned, so much so that one hand was being dressed by a nurse while
he was continually using the other to operate his instrument.
I can testify, my dear sir, that he appeared to be the calmest and most self-possessed
person on board that ship, as I saw him in the glare of the dreadful flames which lit up
the blackest night.
I am an artist and would like to attempt to paint that scene, which has left its lasting
impression upon my soul. I beg that you will allow me to exhibit it for a time in
several of our galleries and finally present it to your family.
Help came none too soon. We were all transferred to other boats, but the sea was
rising, and scarcely had we reached a safe distance when the burning ship slipped into
the sea and disappeared.
I do not know by which boat your son reached the land. In the great confusion I lost
sight of him at last. He has doubtless communicated with you by this time, and I shall
esteem it a great favour if you will put me in communication with him again.
In order that I may do justice to him in the painting I would like to arrange with him a
few sittings while he is in Europe.
Could you kindly send me a photograph of him which will assist me somewhat?
Most sincerely and gratefully yours,
————.

The letter contained several references to mutual acquaintances.

Harold's letters have been frequent and full of the pleasure he is having in
European travel, but the only thing he has said about the voyage is that "it
was not worth so much fuss."

The Country Life Press
Garden City, N. Y.

Transcriber's Notes:
Obvious typos and inconsistencies in spelling have been corrected:

p31. intrument -> instrument
p35. mantain -> maintain
p48. represents the [the] counter-electro-motive force
p64. 2 volts × .1 ampere = .6 watts. -> 6 volts × .1 ampere = .6 watts.
The correct voltage is deduced from the preceding paragraph.
p141. 55 ampere -> .55 ampere
p168. familar -> familiar
p173. preceptible -> perceptible
p229. - p230. countershaft -> counter shaft
p259. H_{2}SO^{4} -> H_{2}SO_{4}
p295. Note C refers to C´ not C´´ and these should be labelled C, and C,, to denote
octaves below middle C.
p316. electri-tricity -> electricity
p356. oufit -> outfit

Throughout the text:

The few cases of "volt-meter" have been changed to "volt meter" which has been
used for the majority of the text.
The single instances of watt meter and watt-meter have been changed to wattmeter
which has been used for the majority of the text.
The few cases of "electro magnet" have been changed to "electro-magnet" which
has been used for the majority of the text.

In the Table of Contents:

Chapter XII page number changed from 118 to 218
Chapter XV name changed from "Electricity from Chemical Action and Chemical
Action from Electricity" to match text which reads "ELECTRIC CURRENTS FROM
CHEMICAL ACTION AND CHEMICAL ACTION FROM ELECTRIC CURRENTS"

In the Table of Illustrations:

"Operating a Switchboard" changed to match caption which reads "Operating the
Switchboard"

p63. The example of Morse code given is correct for "Original" or American Morse. It has
some differences from Continental or International Code which is the current standard.
The spacing of the dots is significant.

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