WARNING: This book of one hundred years ago describes
experiments which are too dangerous to attempt by either
adults or children. It is published for historical
interest only.

The “How-to-do-it” Books

ELECTRICITY FOR BOYS

Fig. 1. WORK BENCH

THE “HOW-TO-DO-IT” BOOKS ELECTRICITY FOR BOYS A working guide, in the successive steps of electricity, described in simple terms WITH MANY ORIGINAL ILLUSTRATIONS By J. S. ZERBE, M.E. AUTHOR OF CARPENTRY FOR BOYSPRACTICAL MECHANICS FOR BOYS THE NEW YORK BOOK COMPANY New York

Copyright, 1914, by

THE NEW YORK BOOK COMPANY

p. i

CONTENTS

p. vii

LIST OF ILLUSTRATIONS

p. 1

INTRODUCTORY

Electricity, like every science, presents two
phases to the student, one belonging to a theoretical
knowledge, and the other which pertains
to the practical application of that knowledge.
The boy is directly interested in the practical use
which he can make of this wonderful phenomenon
in nature.

It is, in reality, the most successful avenue by
which he may obtain the theory, for he learns the
abstract more readily from concrete examples.

It is an art in which shop practice is a greater
educator than can be possible with books. Boys
are not, generally, inclined to speculate or theorize
on phenomena apart from the work itself;
but once put them into contact with the mechanism
itself, let them become a living part of it, and
they will commence to reason and think for themselves.

It would be a dry, dull and uninteresting thing
to tell a boy that electricity can be generated byp. 2
riveting together two pieces of dissimilar metals,
and applying heat to the juncture. But put into
his hands the metals, and set him to perform the
actual work of riveting the metals together, then
wiring up the ends of the metals, heating them,
and, with a galvanometer, watching for results, it
will at once make him see something in the experiment
which never occurred when the abstract
theory was propounded.

He will inquire first what metals should be used
to get the best results, and finally, he will speculate
as to the reasons for the phenomena. When
he learns that all metals are positive-negative or
negative-positive to each other, he has grasped a
new idea in the realm of knowledge, which he
unconsciously traces back still further, only to
learn that he has entered a field which relates to
the constitution of matter itself. As he follows
the subject through its various channels he will
learn that there is a common source of all things;
a manifestation common to all matter, and that all
substances in nature are linked together in a most
wonderful way.

An impulse must be given to a boy’s training.
The time is past for the rule-and-rote method.
The rule can be learned better by a manual application
than by committing a sentence to memory.

In the preparation of this book, therefore, Ip. 3
have made practice and work the predominating
factors. It has been my aim to suggest the best
form in which to do the things in a practical way,
and from that work, as the boy carries it out, to
deduce certain laws and develop the principles
which underlie them. Wherever it is deemed
possible to do so, it is planned to have the boy
make these discoveries for himself, so as to encourage
him to become a thinker and a reasoner
instead of a mere machine.

A boy does not develop into a philosopher or a
scientist through being told he must learn the
principles of this teaching, or the fundamentals
of that school of reasoning. He will unconsciously
imbibe the spirit and the willingness if
we but place before him the tools by which he
may build even the simple machinery that displays
the various electrical manifestations.

p. 5

CHAPTER I

THE STUDY OF ELECTRICITY. HISTORICAL

There is no study so profound as electricity.
It is a marvel to the scientist as well as to the
novice. It is simple in its manifestations, but
most complex in its organization and in its ramifications.
It has been shown that light, heat, magnetism
and electricity are the same, but that they
differ merely in their modes of motion.

First Historical Account.—The first historical
account of electricity dates back to 600 years B. C.
Thales of Miletus was the first to describe the
properties of amber, which, when rubbed, attracted
and repelled light bodies. The ancients
also described what was probably tourmaline, a
mineral which has the same qualities. The torpedo,
a fish which has the power of emitting electric
impulses, was known in very early times.

From that period down to about the year 1600
no accounts of any historical value have been
given. Dr. Gilbert, of England, made a number
of researches at that time, principally with amber
and other materials, and Boyle, in 1650, made
numerous experiments with frictional electricity.

Sir Isaac Newton also took up the subject atp. 6
about the same period. In 1705 Hawksbee made
numerous experiments; also Gray, in 1720, and a
Welshman, Dufay, at about the same time. The
Germans, from 1740 to 1780, made many experiments.
In 1740, at Leyden, was discovered the
jar which bears that name. Before that time, all
experiments began and ended with frictional electricity.

The first attempt to “bottle” electricity was
attempted by Muschenbrœck, at Leyden, who conceived
the idea that electricity in materials might
be retained by surrounding them with bodies which
did not conduct the current. He electrified some
water in a jar, and communication having been
established between the water and the prime conductor,
his assistant, who was holding the bottle,
on trying to disengage the communicating wire,
received a sudden shock.

In 1747 Sir William Watson fired gunpowder by
an electric spark, and, later on, a party from the
Royal Society, in conjunction with Watson, conducted
a series of experiments to determine the
velocity of the electric fluid, as it was then termed.

Benjamin Franklin, in 1750, showed that lightning
was electricity, and later on made his interesting
experiments with the kite and the key.

Discovering Galvanic Electricity.—The great
discovery of Galvani, in 1790, led to the recognitionp. 7
of a new element in electricity, called galvanic
or voltaic (named after the experimenter, Volta),
and now known to be identical with frictional
electricity. In 1805 Poisson was the first to
analyze electricity; and when Œrsted of Copenhagen,
in 1820, discovered the magnetic action of
electricity, it offered a great stimulus to the science,
and paved the way for investigation in a
new direction. Ampere was the first to develop
the idea that a motor or a dynamo could be made
operative by means of the electro-magnetic current;
and Faraday, about 1830, discovered electro-magnetic
rotation.

Electro-magnetic Force.—From this time on
the knowledge of electricity grew with amazing
rapidity. Ohm’s definition of electro-motive
force, current strength and resistance eventuated
into Ohm’s law. Thomson greatly simplified the
galvanometer, and Wheatstone invented the rheostat,
a means of measuring resistance, about
1850. Then primary batteries were brought forward
by Daniels, Grove, Bunsen and Thomson,
and electrolysis by Faraday. Then came the instruments
of precision—the electrometer, the resistance
bridge, the ammeter, the voltmeter—all
of the utmost value in the science.

Measuring Instruments.—The perfection of
measuring instruments did more to advance electricityp. 8
than almost any other field of endeavor;
so that after 1875 the inventors took up the subject,
and by their energy developed and put into
practical operation a most wonderful array of
mechanism, which has become valuable in the
service of man in almost every field of human
activity.

Rapidity of Modern Progress.—This brief history
is given merely to show what wonders have
been accomplished in a few years. The art is
really less than fifty years old, and yet so rapidly
has it gone forward that it is not at all surprising
to hear the remark, that the end of the wonders
has been reached. Less than twenty-five
years ago a high official of the United States
Patent Office stated that it was probable the end
of electrical research had been reached. The
most wonderful developments have been made
since that time; and now, as in the past, one discovery
is but the prelude to another still more remarkable.
We are beginning to learn that we
are only on the threshold of that storehouse in
which nature has locked her secrets, and that
there is no limit to human ingenuity.

How to Acquire the Vast Knowledge.—As the
boy, with his limited vision, surveys this vast
accumulation of tools, instruments and machinery,
and sees what has been and is now beingp. 9
accomplished, it is not to be wondered at that
he should enter the field with timidity. In his
mind the great question is, how to acquire the
knowledge. There is so much to learn. How can
it be accomplished?

The answer to this is, that the student of to-day
has the advantage of the knowledge of all who
have gone before; and now the pertinent thing is
to acquire that knowledge.

The Means Employed.—This brings us definitely
down to an examination of the means that
we shall employ to instil this knowledge, so that
it may become a permanent asset to the student’s
store of information.

The most significant thing in the history of
electrical development is the knowledge that of
all the great scientists not one of them ever added
any knowledge to the science on purely speculative
reasoning. All of them were experimenters.
They practically applied and developed their
theories in the laboratory or the workshop. The
natural inference is, therefore, that the boy who
starts out to acquire a knowledge of electricity,
must not only theorize, but that he shall, primarily,
conduct the experiments, and thereby acquire
the information in a practical way, one example
of which will make a more lasting impression than
pages of dry text

p. 10

Throughout these pages, therefore, I shall, as
briefly as possible, point out the theories involved,
as a foundation for the work, and then illustrate
the structural types or samples; and the work is
so arranged that what is done to-day is merely a
prelude or stepping-stone to the next phase of the
art. In reality, we shall travel, to a considerable
extent, the course which the great investigators
followed when they were groping for the facts
and discovering the great manifestations in
nature.

p. 11

CHAPTER IIToC

WHAT TOOLS AND APPARATUS ARE NEEDED

Preparing the Workshop.—Before commencing
actual experiments we should prepare the
workshop and tools. Since we are going into this
work as pioneers, we shall have to be dependent
upon our own efforts for the production of the
electrical apparatus, so as to be able, with our
home-made factory, to provide the power, the
heat and the electricity. Then, finding we are
successful in these enterprises, we may look forward
for “more worlds to conquer.”

By this time our neighbors will become interested
in and solicit work from us.

Uses of Our Workshops.—They may want us
to test batteries, and it then becomes necessary to
construct mechanism to detect and measure electricity;
to install new and improved apparatus;
and to put in and connect up electric bells in their
houses, as well as burglar alarms. To meet the
requirements, we put in a telegraph line, having
learned, as well as we are able, how they
are made and operated. But we find the telegraph
too slow and altogether unsuited for our
purposes, as well as for the uses of the neighborhood,p. 12
so we conclude to put in a telephone
system.

What to Build.—It is necessary, therefore, to
commence right at the bottom to build a telephone,
a transmitter, a receiver and a switch-board
for our system. From the telephone we
soon see the desirability of getting into touch
with the great outside world, and wireless telegraphy
absorbs our time and energies.

But as we learn more and more of the wonderful
things electricity will do, we are brought into
contact with problems which directly interest the
home. Sanitation attracts our attention. Why
cannot electricity act as an agent to purify our
drinking water, to sterilize sewage and to arrest
offensive odors? We must, therefore, learn something
about the subject of electrolysis.

What to Learn.—The decomposition of water
is not the only thing that we shall describe pertaining
to this subject. We go a step further,
and find that we can decompose metals as well as
liquids, and that we can make a pure metal out
of an impure one, as well as make the foulest
water pure. But we shall also, in the course of
our experiments, find that a cheap metal can be
coated with a costly one by means of electricity—that
we can electroplate by electrolysis.

Uses of the Electrical Devices.—While allp. 13
this is progressing and our factory is turning out
an amazing variety of useful articles, we are led
to inquire into the uses to which we may devote
our surplus electricity. The current may be
diverted for boiling water; for welding metals;
for heating sad-irons, as well as for other purposes
which are daily required.

Tools.—To do these things tools are necessary,
and for the present they should not be expensive.
A small, rigidly built bench is the first requirement.
This may be made, as shown in Fig. 1, of
three 2-inch planks, each 10 inches wide and 6
feet long, mounted on legs 36 inches in height.
In the front part are three drawers for your material,
or the small odds and ends, as well as for such
little tools as you may accumulate. Then you will
need a small vise, say, with a 2-inch jaw, and
you will also require a hand reel for winding
magnets. This will be fully described hereafter.

You can also, probably, get a small, cheap anvil,
which will be of the greatest service in your work.
It should be mounted close up to the work bench.
Two small hammers, one with an A-shaped peon,
and the other with a round peon, should be selected,
and also a plane and a small wood saw with
fine teeth. A bit stock, or a ratchet drill, if you
can afford it, with a variety of small drills; two
wood chisels, say of ⅜-inch and ¾-inch widths;p. 14
small cold chisels; hack saw, 10-inch blade; small
iron square; pair of dividers; tin shears; wire
cutters; 2 pairs of pliers, one flat and the other
round-nosed; 2 awls, centering punch, wire cutters,
and, finally, soldering tools.

Fig. 2.

Fig. 3.
Magnet-winding Reel

If a gas stove is not available, a brazing torch
is an essential tool. Numerous small torches are
being made, which are cheap and easily operated.
A small soldering iron, with pointed end,
should be provided; also metal shears and a small
square; an awl and several sizes of gimlets; a
screwdriver; pair of pliers and wire cutters

p. 15

From the foregoing it will be seen that the cost
of tools is not a very expensive item.

This entire outfit, not including the anvil and
vise, may be purchased new for about $20.00, so
we have not been extravagant.

Magnet-winding Reel.—Some little preparation
must be made, so we may be enabled to handle
our work by the construction of mechanical aids.

Fig. 4. Journal Block.

First of these is the magnet-winding reel, a
plan view of which is shown in Fig. 2. This, for
our present work, will be made wholly of wood.

Select a plank 1½ inches thick and 8 inches
wide, and from this cut off two pieces (A), each
7 inches long, and then trim off the corners (B, B),
as shown in Fig. 4. To serve as the mandrel (C,
Fig. 2), select a piece of broomstick 9 inches long.
Bore a hole (D) in each block (A) a half inch
below the upper margin of the block, this hole
being of such diameter that the broomstick mandrel
will fit and easily turn therein

p. 16

Place a crank (E), 5 inches long, on the outer
end of the mandrel, as in Fig. 3. Then mount
one block on the end of the bench and the other
block 3 inches away. Affix them to the bench by
nails or screws, preferably the latter.

On the inner end of the mandrel put a block
(F) of hard wood. This is done by boring a hole
1 inch deep in the center of the block, into which
the mandrel is driven. On the outer face of the
block is a square hole large enough to receive the
head of a ⅜-inch bolt, and into the depression thus
formed a screw (G) is driven through the block
and into the end of the mandrel, so as to hold the
block (F) and mandrel firmly together. When
these parts are properly put together, the inner
side of the block will rest and turn against the
inner journal block (A).

The tailpiece is made of a 2″ × 4″ scantling
(H), 10 inches long, one end of it being nailed
to a transverse block (I) 2″ × 2″ × 4″. The inner
face of this block has a depression in which is
placed a V-shaped cup (J), to receive the end of
the magnet core (K) or bolt, which is to be used
for this purpose. The tailpiece (H) has a longitudinal
slot (L) 5 inches long adapted to receive
a ½-inch bolt (M), which passes down through
the bench, and is, therefore, adjustable, so it may
be moved to and from the journal bearing (A),p. 17
thereby providing a place for the bolts to be put
in. These bolts are the magnet cores (K), 6
inches long, but they may be even longer, if you
bore several holes (N) through the bench so you
may set over the tailpiece.

With a single tool made substantially like this,
over a thousand of the finest magnets have been
wound. Its value will be appreciated after you
have had the experience of winding a few magnets.

Order in the Workshop.—Select a place for
each tool on the rear upright of the bench, and
make it a rule to put each tool back into its place
after using. This, if persisted in, will soon become
a habit, and will save you hours of time.
Hunting for tools is the unprofitable part of any
work.

p. 18

CHAPTER IIIToC

MAGNETS, COILS, ARMATURES, ETC.

The Two Kinds of Magnet.—Generally speaking,
magnets are of two kinds, namely, permanent
and electro-magnetic.

Permanent Magnets.—A permanent magnet is
a piece of steel in which an electric force is exerted
at all times. An electro-magnet is a piece
of iron which is magnetized by a winding of wire,
and the magnet is energized only while a current
of electricity is passing through the wire.

Electro-Magnet.—The electro-magnet, therefore,
is the more useful, because the pull of the
magnet can be controlled by the current which
actuates it.

The electro-magnet is the most essential of all
contrivances in the operation and use of electricity.
It is the piece of mechanism which does
the physical work of almost every electrical apparatus
or machine. It is the device which has
the power to convert the unseen electric current
into motion which may be observed by the human
eye. Without it electricity would be a useless
agent to man.

While the electro-magnet is, therefore, the formp. 19
of device which is almost wholly used, it is necessary,
first, to understand the principles of the
permanent magnet.

Magnetism.—The curious force exerted by a
magnet is called magnetism, but its origin has
never been explained. We know its manifestations
only, and laws have been formulated to explain
its various phases; how to make it more or
less intense; how to make its pull more effective;
the shape and form of the magnet and the material
most useful in its construction.

Fig 5. Plain Magnet Bar

Materials for Magnets.—Iron and steel are the
best materials for magnets. Some metals are non-magnetic,
this applying to iron if combined with
manganese. Others, like sulphur, zinc, bismuth,
antimony, gold, silver and copper, not only are
non-magnetic, but they are actually repelled by
magnetism. They are called the diamagnetics.

Non-magnetic Materials.—Any non-magnetic
body in the path of a magnetic force does not
screen or diminish its action, whereas a magnetic
substance will

p. 20

In Fig. 5 we show the simplest form of magnet,
merely a bar of steel (A) with the magnetic
lines of force passing from end to end. It will
be understood that these lines extend out on all
sides, and not only along two sides, as shown in
the drawing. The object is to explain clearly
how the lines run.

Fig 6. Severed Magnet

Action of a Severed Magnet.—Now, let us suppose
that we sever this bar in the middle, as in Fig. 6,
or at any other point between the ends. In this
case each part becomes a perfect magnet, and a
new north pole (N) and a new south pole (S) are
made, so that the movement of the magnetic lines
of force are still in the same direction in each—that
is, the current flows from the north pole to
the south pole.

What North and South Poles Mean.—If these
two parts are placed close together they will attract
each other. But if, on the other hand, one
of the pieces is reversed, as in Fig. 7, they will
repel each other. From this comes the statement
that likes repel and unlikes attract each other

p. 21

Repulsion and Attraction.—This physical act
of repulsion and attraction is made use of in
motors, as we shall see hereinafter.

It will be well to bear in mind that in treating
of electricity the north pole is always associated
with the plus sign (+) and the south pole with
the minus sign (-). Or the N sign is positive
and the S sign negative electricity.

Fig. 7. Reversed Magnets

Positives and Negatives.—There is really no
difference between positive and negative electricity,
so called, but the foregoing method merely
serves as a means of identifying or classifying the
opposite ends of a magnet or of a wire.

Magnetic Lines of Force.—It will be noticed
that the magnetic lines of force pass through the
bar and then go from end to end through the atmosphere.
Air is a poor conductor of electricity,
so that if we can find a shorter way to conduct
the current from the north pole to the south pole,
the efficiency of the magnet is increased.

This is accomplished by means of the well-knownp. 22
horseshoe magnet, where the two ends
(N, S) are brought close together, as in Fig. 8.

The Earth as a Magnet.—The earth is a huge
magnet and the magnetic lines run from the north
pole to the south pole around all sides of the globe.

Fig. 8. Horseshoe Magnet

The north magnetic pole does not coincide with
the true north pole or the pivotal point of the
earth’s rotation, but it is sufficiently near for all
practical purposes. Fig. 9 shows the magnetic
lines running from the north to the south pole.

Why the Compass Points North and South.—Now,
let us try to ascertain why the compass
points north and south.

Let us assume that we have a large magnet (A,
Fig. 10), and suspend a small magnet (B)
above it, so that it is within the magnetic field of
the large magnet. This may be done by means of
a short pin (C), which is located in the middlep. 23
of the magnet (B), the upper end of this pin
having thereon a loop to which a thread (D) is
attached. The pin also carries thereon a pointer
(E), which is directed toward the north pole of
the bar (B).

Fig. 9. Earth’s Magnetic Lines

You will now take note of the interior magnetic
lines (X), and the exterior magnetic lines (Z)
of the large magnet (A), and compare the direction
of their flow with the similar lines in the
small magnet (B).

The small magnet has both its exterior and its
interior lines within the exterior lines (Z) of the
large magnet (A), so that as the small magnet
(B) is capable of swinging around, the N pole ofp. 24
the bar (B) will point toward the S pole of the
larger bar (A). The small bar, therefore, is influenced
by the exterior magnetic field (Z).

Fig. 10. Two Permanent Magnets

Fig. 11. Magnets in the Earth’s Magnetic Field

Let us now take the outline represented by the
earth’s surface (Fig. 11), and suspend a magnet
(A) at any point, like the needle of a compass,
and it will be seen that the needle will arrange
itself north and south, within the magnetic field
which flows from the north to the south pole

p. 25

Peculiarity of a Magnet.—One characteristic
of a magnet is that, while apparently the magnetic
field flows out at one end of the magnet, and
moves inwardly at the other end, the power of
attraction is just the same at both ends.

In Fig. 12 are shown a bar (A) and a horseshoe
magnet (B). The bar (A) has metal blocks (C)
at each end, and each of these blocks is attracted
to and held in contact with the ends by magnetic
influence, just the same as the bar (D) is attracted
by and held against the two ends of the horseshoe
magnet. These blocks (C) or the bar (D) are
called armatures. Through them is represented
the visible motion produced by the magnetic field.

Fig. 12. Armatures for Magnets

Action of the Electro-Magnet.—The electro-magnet
exerts its force in the same manner
as a permanent magnet, so far as attraction and
repulsion are concerned, and it has a north and
a south pole, as in the case with the permanent
magnet. An electro-magnet is simply a bar ofp. 26
iron with a coil or coils of wire around it; when
a current of electricity flows through the wire, the
bar is magnetized. The moment the current is
cut off, the bar is demagnetized. The question
that now arises is, why an electric current flowing
through a wire, under those conditions, magnetizes
the bar, or core, as it is called.

Fig. 13. Magnetized Field

Fig. 14. Magnetized Bar

In Fig. 13 is shown a piece of wire (A). Let
us assume that a current of electricity is flowing
through this wire in the direction of the darts.
What actually takes place is that the electricity
extends out beyond the surface of the wire in the
form of the closed rings (B). If, now, this wire
(A) is wound around an iron core (C, Fig.
14), you will observe that this electric field, asp. 27
it is called, entirely surrounds the core, or rather,
that the core is within the magnetic field or influence
of the current flowing through the wire, and
the core (C) thereby becomes magnetized, but
it is magnetized only when the current passes
through the wire coil (A).

Fig. 15. Direction of Current

From the foregoing, it will be understood that
a wire carrying a current of electricity not only
is affected within its body, but that it also has a
sphere of influence exteriorly to the body of the
wire, at all points; and advantage is taken of
this phenomenon in constructing motors, dynamos,
electrical measuring devices and almost
every kind of electrical mechanism in existence.

Exterior Magnetic Influence Around a Wire
Carrying a Current.—Bear in mind that the wire
coil (A, Fig. 14) does not come into contact with
the core (C). It is insulated from the core, either
by air or by rubber or other insulating substance,
and a current passing from A to C under those
conditions is a current of induction. On the other
hand, the current flowing through the wire (A)p. 28
from end to end is called a conduction current.
Remember these terms.

In this connection there is also another thing
which you will do well to bear in mind. In Fig.
15 you will notice a core (C) and an insulated
wire coil (B) wound around it. The current,
through the wire (B), as shown by the darts (D),
moves in one direction, and the induced current in
the core (C) travels in the opposite direction, as
shown by the darts (D).

Fig. 16. Direction of Induction Current

Parallel Wires.—In like manner, if two wires
(A, B, Fig. 16) are parallel with each other, and
a current of electricity passes along the wire (A)
in one direction, the induced current in the wire
(B) will move in the opposite direction.

These fundamental principles should be thoroughly
understood and mastered.

p. 29

CHAPTER IVToC

FRICTIONAL, VOLTAIC OR GALVANIC, AND ELECTRO-MAGNETIC ELECTRICITY

Three Electrical Sources.—It has been found
that there are three kinds of electricity, or, to be
more accurate, there are three ways to generate it.
These will now be described.

When man first began experimenting, he produced
a current by frictional means, and collected
the electricity in a bottle or jar. Electricity, so
stored, could be drawn from the jar, by attaching
thereto suitable connection. This could be effected
only in one way, and that was by discharging
the entire accumulation instantaneously. At that
time they knew of no means whereby the current
could be made to flow from the jar as from a battery
or cell.

Frictional Electricity.—With a view of explaining
the principles involved, we show in Fig.
17 a machine for producing electricity by friction.

Fig. 17. Friction-Electricity Machine

This is made up as follows: A represents the
base, having thereon a flat member (B), on which
is mounted a pair of parallel posts or standards
(C, C), which are connected at the top by a cross
piece (D). Between these two posts is a glassp. 30
disc (E), mounted upon a shaft (F), which passes
through the posts, this shaft having at one end a
crank (G). Two leather collecting surfaces (H,
H), which are in contact with the glass disc (E),
are held in position by arms (I, J), the arm (I)
being supported by the cross piece (D), and the
arm (J) held by the base piece (B). A rod (K),
U-shaped in form, passes over the structure here
thus described, its ends being secured to the basep. 31
(B). The arms (I, J) are both electrically connected
with this rod, or conductor (K), joined to
a main conductor (L), which has a terminating
knob (M). On each side and close to the terminal
end of each leather collector (H) is a fork-shaped
collector (N). These two collectors are also connected
electrically with the conductor (K). When
the disc is turned electricity is generated by the
leather flaps and accumulated by the collectors
(N), after which it is ready to be discharged at the
knob (M).

In order to collect the electricity thus generated
a vessel called a Leyden jar is used.

Leyden Jar.—This is shown in Fig. 18. The jar
(A) is of glass coated exteriorly at its lower end
with tinfoil (B), which extends up a little more
than halfway from the bottom. This jar has a
wooden cover or top (C), provided centrally with
a hole (D). The jar is designed to receive within
it a tripod and standard (E) of lead. Within this
lead standard is fitted a metal rod (F), which projects
upwardly through the hole (D), its upper
end having thereon a terminal knob (G). A sliding
cork (H) on the rod (F) serves as a means to
close the jar when not in use. When in use this
cork is raised so the rod may not come into contact,
electrically, with the cover (C).

The jar is half filled with sulphuric acid (I),p. 32
after which, in order to charge the jar, the knob
(G) is brought into contact with the knob (M) of
the friction generator (Fig. 17).

Voltaic or Galvanic Electricity.—The second
method of generating electricity is by chemical
means, so called, because a liquid is used as one
of the agents.

Fig. 18. Leyden Jar

Galvani, in 1790, made the experiments which
led to the generation of electricity by means of
liquids and metals. The first battery was called
the “crown of cups,” shown in Fig. 19, and consistingp. 33
of a row of glass cups (A), containing salt
water. These cups were electrically connected by
means of bent metal strips (B), each strip having
at one end a copper plate (C), and at the other
end a zinc plate (D). The first plate in the cup
at one end is connected with the last plate in the
cup at the other end by a conductor (E) to make
a complete circuit.

Fig. 19. Galvanic Electricity. Crown of Cups

The Cell and Battery.—From the foregoing it
will be seen that within each cup the current flows
from the zinc to the copper plates, and exteriorly
from the copper to the zinc plates through the
conductors (B and E).

A few years afterwards Volta devised what is
known as the voltaic pile (Fig. 20).

Voltaic Pile—How Made.—This is made of alternate
discs of copper and zinc with a piece ofp. 34
cardboard of corresponding size between each zinc
and copper plate. The cardboard discs are moistened
with acidulated water. The bottom disc of
copper has a strip which connects with a cup of
acid, and one wire terminal (A) runs therefrom.
The upper disc, which is of zinc, is also connected,
by a strip, with a cup of acid from which extends
the other terminal wire (B).

Fig. 20. Voltaic Electricity

Plus and Minus Signs.—It will be noted that
the positive or copper disc has the plus signp. 35
(+) while the zinc disc has the minus (-) sign.
These signs denote the positive and the negative
sides of the current.

The liquid in the cells, or in the moistened
paper, is called the electrolyte and the plates or
discs are called electrodes. To define them more
clearly, the positive plate is the anode, and the
negative plate the cathode.

The current, upon entering the zinc plate, decomposes
the water in the electrolyte, thereby
forming oxygen. The hydrogen in the water,
which has also been formed by the decomposition,
is carried to the copper plate, so that the plate
finally is so coated with hydrogen that it is difficult
for the current to pass through. This condition
is called “polarization,” and to prevent it has
been the aim of all inventors. To it also we may
attribute the great variety of primary batteries,
each having some distinctive claim of merit.

The Common Primary Cell.—The most common
form of primary cell contains sulphuric acid,
or a sulphuric acid solution, as the electrolyte,
with zinc for the anode, and carbon, instead of copper,
for the cathode.

The ends of the zinc and copper plates are
called terminals, and while the zinc is the anode
or positive element, its terminal is designated as
the positive pole. In like manner, the carbon isp. 36
the negative element or cathode, and its terminal
is designated as negative pole.

Fig. 21 will show the relative arrangement of
the parts. It is customary to term that end or element
from which the current flows as positive.
A cell is regarded as a whole, and as the current
passes out of the cell from the copper element, the
copper terminal becomes positive.

Fig. 21. Primary Battery

Battery Resistance, Electrolyte and Current.—The
following should be carefully memorized:

A cell has reference to a single vessel. When
two or more cells are coupled together they form
a battery

p. 37

Resistance is opposition to the movement of the
current. If it is offered by the electrolyte, it is
designated “Internal Resistance.” If, on the other
hand, the opposition takes place, for instance,
through the wire, it is then called “External Resistance.”

The electrolyte must be either acid, or alkaline,
or saline, and the electrodes must be of dissimilar
metals, so the electrolyte will attack one of them.

The current is measured in amperes, and the
force with which it is caused to flow is measured
in volts. In practice the word “current” is used
to designate ampere flow; and electromotive force,
or E. M. F., is used instead of voltage.

Electro-magnetic Electricity.—The third
method of generating electricity is by electro-magnets.
The value and use of induction will now
be seen, and you will be enabled to utilize the lesson
concerning magnetic action referred to in the
previous chapter.

Magnetic Radiation.—You will remember that
every piece of metal which is within the path of
an electric current has a space all about its surface
from end to end which is electrified. This
electrified field extends out a certain distance from
the metal, and is supposed to maintain a movement
around it. If, now, another piece of metal is
brought within range of this electric or magneticp. 38
zone and moved across it, so as to cut through this
field, a current will be generated thereby, or rather
added to the current already exerted, so that if
we start with a feeble current, it can be increased
by rapidly “cutting the lines of force,” as it is
called.

Different Kinds of Dynamo.—While there are
many kinds of dynamo, they all, without exception,
are constructed in accordance with this principle.
There are also many varieties of current.
For instance, a dynamo may be made to produce
a high voltage and a low amperage; another with
high amperage and low voltage; another which
gives a direct current for lighting, heating, power,
and electroplating; still another which generates
an alternating current for high tension power, or
transmission, arc-lighting, etc., all of which will
be explained hereafter.

In this place, however, a full description of a direct-current
dynamo will explain the principle involved
in all dynamos—that to generate a current
of electricity makes it necessary for us to move
a field of force, like an armature, rapidly and continuously
through another field of force, like a
magnetic field.

Direct-Current Dynamo.—We shall now make
the simplest form of dynamo, using for this purpose
a pair of permanent magnets

p. 39

Fig. 22. Dynamo Field and Pole Piece

Simple Magnet Construction.—A simple way
to make a pair of magnets for this purpose is
shown in Fig. 22. A piece of round ¾-inch steel
core (A), 5½ inches long, is threaded at both ends
to receive at one end a nut (B), which is screwed
on a sufficient distance so that the end of the core
(A) projects a half inch beyond the nut. The
other end of the steel core has a pole piece ofp. 40
iron (C) 2″ × 2″ × 4″, with a hole midway between
the ends, threaded entirely through, and provided
along one side with a concave channel, within
which the armature is to turn. Now, before the
pole piece (C) is put on, we will slip on a disc
(E), made of hard rubber, then a thin rubber tube
(F), and finally a rubber disc (G), so as to provide
a positive insulation for the wire coil which
is wound on the bobbin thus made.

How to Wind.—In practice, and as you go further
along in this work, you will learn the value,
first, of winding one layer of insulated wire on the
spool, coating it with shellac, and then putting
on the next layer, and so on; when completely
wound, the two wire terminals may be brought
out at one end; but for our present purpose, and
to render the explanation clearer, the wire terminals
are at the opposite ends of the spool (H, H’).

The Dynamo Fields.—Two of these spools are
so made and they are called the fields of the dynamo.

We will next prepare an iron bar (I), 5 inches
long and ½ inch thick and 1½ inches wide, then
bore two holes through it so the distance measures
3 inches from center to center. These holes are
to be threaded for the ¾-inch cores (A). This
bar holds together the upper ends of the cores,
as shown in Fig. 23

p. 41

Fig. 23. Base and Fields Assembled

We then prepare a base (J) of any hard wood,
2 inches thick, 8 inches long and 8 inches wide,p. 42
and bore two ¾-inch holes 3 inches apart on a middle
line, to receive a pair of ¾-inch cap screws (K),
which pass upwardly through the holes in the base
and screw into the pole pieces (C). A wooden bar
(L), 1½” × 1½”, 8 inches long, is placed under each
pole piece, which is also provided with holes for
the cap screws (K). The lower side of the base
(J) should be countersunk, as at M, so the head
of the nut will not project. The fields of the dynamo
are now secured in position to the base.

Figs. 24-25. Details of the Armature

The Armature.—A bar of iron (Fig. 24), 1″ × 1″
and 2¼ inches long, is next provided. Through this
bar (1) are then bored two 5/16-inch holes 1¾
inches apart, and on the opposite sides of this bar
are two half-rounded plates of iron (3) (Fig. 25).

Armature Winding.—Each plate is ½ inch thick,
1¾ inches wide and 4 inches long, each plate having
holes (4) to coincide with the holes (2) of the
bar (1), so that when the two plates are applied top. 43
opposite sides of the bar, and riveted together,
a cylindrical member is formed, with two channels
running longitudinally, and transversely at the
ends; and in these channels the insulated wires
are wound from end to end around the central
block (1).

Mounting the Armature.—It is now necessary
to provide a means for revolving this armature.
To this end a brass disc (5, Fig. 26) is made, 2
inches in diameter, ⅛ inch thick. Centrally, at one
side, is a projecting stem (6) of round brass,
which projects out 2 inches, and the outer end is
turned down, as at 7, to form a small bearing
surface.

Figs. 26-27. Armature Mountings

The other end of the armature has a similar
disc (8), with a central stem (9), 1½ inches long,
turned down to ¼-inch diameter up to within ¼
inch of the disc (7), so as to form a shoulder

p. 44

The Commutator.—In Fig. 27 is shown, at 10,
a wooden cylinder, 1 inch long and 1¼ inches in
diameter, with a hole (11) bored through axially,
so that it will fit tightly on the stem (6) of the
disc (5). On this wooden cylinder is driven a
brass or copper tube (12), which has holes (13)
opposite each other. Screws are used to hold
the tube to the wooden cylinder, and after they are
properly secured together, the tube (12) is cut by
a saw, as at 14, so as to form two independent
tubular surfaces

p. 45

Fig. 28.
End View Armature, Mounted

These tubular sections are called the commutator
plates.

Fig. 29.
Top View of Armature on Base

In order to mount this armature, two bearings
are provided, each comprising a bar of brass (15,
Fig. 28), each ¼ inch thick, ½ inch wide and 4½
inches long. Two holes, 3 inches apart, are
formed through this bar, to receive round-headed
wood screws (16), these screws being 3 inches
long, so they will pass through the wooden piecesp. 46
(I) and enter the base (J). Midway between the
ends, each bar (15) has an iron bearing block (17),
¾” × ½” and 1½ inches high, the ¼-inch hole for the
journal (7) being midway between its ends.

Commutator Brushes.—Fig. 28 shows the base,
armature and commutator assembled in position,
and to these parts have been added the commutator
brushes. The brush holder (18) is a horizontal
bar made of hard rubber loosely mounted
upon the journal pin (7), which is 2½ inches long.
At each end is a right-angled metal arm (19) secured
to the bar (18) by screws (20). To these
arms the brushes (21) are attached, so that their
spring ends engage with the commutator (12).
An adjusting screw (22) in the bearing post (17),
with the head thereof bearing against the brush-holder
(18), serves as a means for revolubly adjusting
the brushes with relation to the commutator.

Dynamo Windings.—There are several ways to
wind the dynamos. These can be shown better by
the following diagrams (Figs. 30, 31, 32, 33):

The Field.—If the field (A, Fig. 30) is not a
permanent magnet, it must be excited by a cell or
battery, and the wires (B, B’) are connected up
with a battery, while the wires (C, C’) may be connected
up to run a motor. This would, therefore,
be what is called a “separately excited” dynamo.p. 47
In this case the battery excites the field and the
armature (D), cutting the lines of force at the
pole pieces (E), so that the armature gathers
the current for the wires (C, C’).

Figs. 30-31. Field Winding, Series-wound

Series-wound Field.—Fig. 31 shows a “series-wound”
dynamo. The wires of the fields
(A) are connected up in series with the brushes
of the armature (D), and the wires (G, G’) are
led out and connected up with a lamp, motor
or other mechanism. In this case, as well as in
Figs. 32 and 33, both the field and the armature
are made of soft gray iron. With this winding
and means of connecting the wires, the field is
constantly excited by the current passing through
the wires.

Shunt-wound Field.—Fig. 32 represents what
is known as a “shunt-wound” dynamo. Here thep. 48
field wires (H, H) connect with the opposite
brushes of the armature, and the wires (I, I’) are
also connected with the brushes, these two wires
being provided to perform the work required.
This is a more useful form of winding for electroplating
purposes.

Figs. 32-33. Shunt-wound, Compound-wound

Compound-wound Field.—Fig. 33 is a diagram
of a “compound-wound” dynamo. The regular
field winding (J) has its opposite ends connected
directly with the armature brushes. There is
also a winding, of a comparatively few turns, of
a thicker wire, one terminal (K) of which is connected
with one of the brushes and the other terminal
(K’) forms one side of the lighting circuit.
A wire (L) connects with the other armature
brush to form a complete lighting circuit.

p. 49

CHAPTER VToC

HOW TO DETECT AND MEASURE ELECTRICITY

Measuring Instruments.—The production of
an electric current would not be of much value
unless we had some way by which we might detect
and measure it. The pound weight, the foot rule
and the quart measure are very simple devices,
but without them very little business could be
done. There must be a standard of measurement
in electricity as well as in dealing with iron or
vegetables or fabrics.

As electricity cannot be seen by the human eye,
some mechanism must be made which will reveal
its movements.

The Detector.—It has been shown in the preceding
chapter that a current of electricity passing
through a wire will cause a current to pass
through a parallel wire, if the two wires are
placed close together, but not actually in contact
with each other. An instrument which reveals
this condition is called a galvanometer. It not
only detects the presence of a current, but it
shows the direction of its flow. We shall now see
how this is done.

For example, the wire (A, Fig. 35) is connectedp. 50
up in an electric circuit with a permanent magnet
(B) suspended by a fine wire (C), so that
the magnet (B) may freely revolve.

Figs. 34-36.
To the right, Compass Magnet, To the left

For convenience, the magnetic field is shown
flowing in the direction of the darts, in which the
dart (D) represents the current within the magnet
(B) flowing toward the north pole, and the
darts (E) showing the exterior current flowing
toward the south pole. Now, if the wire (A) is
brought up close to the magnet (B), and a current
passed through A, the magnet (B) will be
affected. Fig. 35 shows the normal condition of
the magnetized bar (B) parallel with the wire
(A) when a current is not passing through the
latter.

Direction of Current.—If the current should
go through the wire (A) from right to left,
as shown in Fig. 34, the magnet (B) would
swing in the direction taken by the hands
of a clock and assume the position shownp. 51
in Fig. 34. If, on the other hand, the current
in the wire (A) should be reversed or flow
from left to right, the magnet (B) would swing
counter-clock-wise, and assume the position shown
in Fig. 36. The little pointer (G) would, in either
case, point in the direction of the flow of the current
through the wire (A).

Fig. 37. Indicating Direction of Current

p. 52

Simple Current Detector.—A simple current
detector may be made as follows:

Prepare a base 3′ × 4′ in size and 1 inch thick.
At each corner of one end fix a binding post, as at
A, A’, Fig. 37. Then select 20 feet of No. 28 cotton-insulated
wire, and make a coil (B) 2 inches
in diameter, leaving the ends free, so they may be
affixed to the binding posts (A, A’). Now glue
or nail six blocks (C) to the base, each block being
1″ × 1″ × 2″, and lay the coil on these blocks. Then
drive an L-shaped nail (D) down into each block,
on the inside of the coil, as shown, so as to hold
the latter in place.

Fig. 38. The Bridge

Now make a bridge (E, Fig. 38) of a strip of
brass ½ inch wide, 1/16 inch thick and long enough
to span the coil, and bend the ends down, as at
F, so as to form legs. A screw hole (G) is
formed in each foot, so it may be screwed to the
base.

Midway between the ends this bridge has a transverse
slot (H) in one edge, to receive therein thep. 53
pivot pin of the swinging magnet. In order to
hold the pivot pin in place, cut out an H-shaped
piece of sheet brass (I), which, when laid on the
bridge, has its ends bent around the latter, as
shown at J, and the crossbar of the H-shaped
piece then will prevent the pivot pin from coming
out of the slot (H).

Fig. 39. Details of Detector

The magnet is made of a bar of steel (K, Fig.
39) 1½ inches long, ⅜ inch wide and 1/16 inch
thick, a piece of a clock spring being very serviceable
for this purpose. The pivot pin is made of
an ordinary pin (L), and as it is difficult to
solder the steel magnet (K) to the pin, solder
only a small disc (M) to the pin (L). Then bore
a hole (N) through the middle of the magnet (K),
larger in diameter than the pin (L), and, after
putting the pin in the hole, pour sealing wax into
the hole, and thereby secure the two parts together.
Near the upper end of the pin (L) solder
the end of a pointer (O), this pointer being at
right angles to the armature (K). It is betterp. 54
to have a metal socket for the lower end of the
pin. When these parts are put together, as shown
in Fig. 37, a removable glass top, or cover, should
be provided.

This is shown in Fig. 40, in which a square,
wooden frame (P) is used, and a glass (Q) fitted
into the frame, the glass being so arranged that
when the cover is in position it will be in close
proximity to the upper projecting end of the pivot
pin (L), and thus prevent the magnet from becoming
misplaced.

Fig. 40. Cross Section of Detector

How to Place the Detector.—If the detector
is placed north and south, as shown by the two
markings, N and S (Fig. 37), the magnet bar will
point north and south, being affected by the earth’s
magnetism; but when a current of electricity flows
through the coil (B), the magnet will be deflected
to the right or to the left, so that the pointer
(O) will then show the direction in which thep. 55
current is flowing through the wire (R) which
you are testing.

The next step of importance is to measure the
current, that is, to determine its strength or intensity,
as well as the flow or quantity.

Different Ways of Measuring a Current.—There
are several ways to measure the properties
of a current, which may be defined as follows:

1. The Sulphuric Acid Voltameter.—By
means of an electrolytic action, whereby the current
decomposes an acidulated solution—that is,
water which has in it a small amount of sulphuric
acid—and then measuring the gas generated by
the current.

2. The Copper Voltameter.—By electro-chemical
means, in which the current passes through
plates immersed in a solution of copper sulphate.

3. The Galvanoscope.—By having a coil of insulated
wire, with a magnet suspended so as to
turn freely within the coil, forming what is called
a galvanoscope.

4. Electro-magnetic Method.—By using a
pair of magnets and sending a current through
the coils, and then measuring the pull on the armature.

5. The Power or Speed Method.—By using an
electric fan, and noting the revolutions produced
by the current

p. 56

6. The Calorimeter.—By using a coil of bare
wire, immersed in paraffine oil, and then measuring
the temperature by means of a thermometer.

Fig. 41. Acid Voltameter	Fig. 42. Copper Voltameter

7. The Light Method.—Lastly, by means of
an electric light, which shows, by its brightness, a
greater or less current.

The Preferred Methods.—It has been found
that the first and second methods are the onlyp. 57
ones which will accurately register current
strength, and these methods have this advantage—that
the chemical effect produced is not dependent
upon the size or shape of the apparatus or
the plates used.

How to Make a Sulphuric Acid Voltameter.—In
Fig. 41 is shown a simple form of sulphuric
acid voltameter, to illustrate the first method. A
is a jar, tightly closed by a cover (B). Within
is a pair of platinum plates (C, C), each having
a wire (D) through the cover. The cover has
a vertical glass tube (E) through it, which extends
down to the bottom of the jar, the electrolyte
therein being a weak solution of sulphuric
acid. When a current passes through the wires
(D), the solution is partially decomposed—that is,
converted into gas, which passes up into the
vacant space (F) above the liquid, and, as
it cannot escape, it presses the liquid downwardly,
and causes the latter to flow upwardly
into the tube (E). It is then an easy matter,
after the current is on for a certain time,
to determine its strength by the height of the
liquid in the tube.

How to Make a Copper Voltameter.—The second,
or copper voltameter, is shown in Fig. 42.
The glass jar (A) contains a solution of copper
sulphate, known in commerce as blue vitriol. Ap. 58
pair of copper plates (B, B’) are placed in this
solution, each being provided with a connecting
wire (C). When a current passes through the
wires (C), one copper plate (B) is eaten away
and deposited on the other plate (B’). It is then
an easy matter to take out the plates and find out
how much in weight B’ has gained, or how much
B has lost.

In this way, in comparing the strength of, say,
two separate currents, one should have each current
pass through the voltameter the same length
of time as the other, so as to obtain comparative
results.

It is not necessary, in the first and second methods,
to consider the shapes, the sizes of the plates
or the distances between them. In the first
method the gas produced, within a given time,
will be the same, and in the second method the
amount deposited or eaten away will be the same
under all conditions.

Disadvantages of the Galvanoscope.—With the
third method (using the galvanoscope) it is necessary,
in order to get a positively correct reading
instrument, to follow an absolutely accurate plan
in constructing each part, in every detail, and
great care must be exercised, particularly in winding.
It is necessary also to be very careful inp. 59
selecting the sizes of wire used and in the number
of turns made in the coils.

This is equally true of the fourth method, using
the electro-magnet, because the magnetic pull is
dependent upon the size of wire from which the
coils are made and the number of turns of wire.

Objections to the Calorimeter.—The calorimeter,
or sixth method, has the same objection.
The galvanoscope and electro-magnet do not respond
equally to all currents, and this is also true,
even to a greater extent, with the calorimeter.

p. 60

CHAPTER VIToC

VOLTS, AMPERES, OHMS AND WATTS

Understanding Terms.—We must now try to
ascertain the meaning of some of the terms
so frequently used in connection with electricity.
If you intended to sell or measure produce or
goods of any kind, it would be essential to know
how many pints or quarts are contained in a
gallon, or in a bushel, or how many inches there
are in a yard, and you also ought to know just
what the quantity term bushel or the measurement
yard means.

Intensity and Quantity.—Electricity, while it
has no weight, is capable of being measured by
means of its intensity, or by its quantity. Light
may be measured or tested by its brilliancy. If
one light is of less intensity than another and both
of them receive their impulses from the same
source, there must be something which interferes
with that light which shows the least brilliancy.
Electricity can also be interfered with, and this
interference is called resistance.

Voltage.—Water may be made to flow with
greater or less force, or velocity, through a pipe,
the degree of same depending upon the height ofp. 61
the water which supplies the pipe. So with electricity.
It may pass over a wire with greater or
less force under one condition than another. This
force is called voltage. If we have a large pipe,
a much greater quantity of water will flow through
it than will pass through a small pipe, providing
the pressure in each case is alike. This quantity
in electricity is called amperage.

In the case of water, a column 1″ × 1″, 28
inches in height, weighs 1 pound; so that if a
pipe 1 inch square draws water from the bottom
it flows with a pressure of 1 pound. If the pipe
has a measurement of 2 square inches, double the
quantity of water will flow therefrom, at the same
pressure.

Amperage.—If, on the other hand, we have a
pipe 1 inch square, and there is a depth of 56
inches of water in the reservoir, we shall get as
much water from the reservoir as though we had
a pipe of 2 square inches drawing water from a
reservoir which is 28 inches deep.

Meaning of Watts.—It is obvious, therefore,
that if we multiply the height of the water in inches
with the area of the pipe, we shall obtain a factor
which will show how much water is flowing.

Here are two examples:

1. p. 6228 inches = height of the water in the reservoir.
   2 square inches = size of the pipe.
   Multiply 28 × 2 = 56.
2. 56 = height of the water in the reservoir.
   1 square inch = size of the pipe.
   Multiply 56 × 1 = 56.

Thus the two problems are equal.

A Kilowatt.—Now, in electricity, remembering
that the height of the water corresponds with voltage
in electricity, and the size of the pipe with
amperage, if we multiply volts by amperes, or amperes
by volts, we get a result which is indicated
by the term watts. One thousand of these watts
make a kilowatt, and the latter is the standard
of measurement by which a dynamo or motor is
judged or rated.

Thus, if we have 5 amperes and 110 volts, the
result of multiplying them would be 550 watts,
or 5 volts and 110 amperes would produce 550
watts.

A Standard of Measurement.—But with all
this we must have some standard. A bushel
measure is of a certain size, and a foot has a
definite length, so in electricity there is a recognized
force and quantity which are determined
as follows:

The Ampere Standard.—It is necessary, first,
to determine what an ampere is. For this purpose
a standard solution of nitrate of silver isp. 63
used, and a current of electricity is passed through
this solution. In doing so the current deposits
silver at the rate of 0.001118 grains per second for
each ampere.

The Voltage Standard.—In order to determine
the voltage we must know something of resistance.
Different metals do not transmit a current with
equal ease. The size of a conductor, also, is an
important factor in the passage of a current. A
large conductor will transmit a current much better
than a small conductor. We must therefore
have a standard for the ohm, which is the measure
of resistance.

The Ohm.—It is calculated in this way: There
are several standards, but the one most generally
employed is the International Ohm. To determine
it, by this system, a column of pure mercury,
106.3 millimeters long and weighing 14.4521
grams, is used. This would make a square tube
about 94 inches long, and a little over 1/25 of
an inch in diameter. The resistance to a current
flow in such a column would be equal to 1
ohm.

Calculating the Voltage.—In order to arrive
at the voltage we must use a conductor, which,
with a resistance of 1 ohm, will produce 1 ampere.
It must be remembered that the volt is the
practical unit of electro-motive force

p. 64

While it would be difficult for the boy to conduct
these experiments in the absence of suitable
apparatus, still, it is well to understand thoroughly
how and why these standards are made
and used.

p. 65

CHAPTER VIIToC

PUSH BUTTONS, SWITCHES, ANNUNCIATORS, BELLS AND LIKE APPARATUS

Simple Switches.—We have now gone over the
simpler or elementary outlines of electrical phenomena,
and we may commence to do some of the
practical work in the art. We need certain apparatus
to make connections, which will be constructed
first.

A Two-Pole Switch.—A simple two-pole switch
for a single line is made as follows:

A base block (A, Fig. 43) 3 inches long, 2 inches
wide and ¾ inch thick, has on it, at one end, a
binding screw (B), which holds a pair of fingers
(C) of brass or copper, these fingers being bent
upwardly and so arranged as to serve as fingers to
hold a switch bar (D) between them. This bar
is also of copper or brass and is pivoted to the
fingers. Near the other end of the base is a
similar binding screw (E) and fingers (F) to receive
the blade of the switch bar. The bar has a
handle (G) of wood. The wires are attached to
the respective binding screws (B, E).

Double-Pole Switch.—A double-pole switch
or a switch for a double line is shown in Fig. 44.p. 66
This is made similar in all respects to the one
shown in Fig. 43, excepting that there are two
switch blades (A, A) connected by a cross bar
(B) of insulating material, and this bar carries
the handle (C).

Fig. 43. Two-Pole Switch

Fig. 44. Double-Pole Switch

Other types of switch will be found very useful.
In Fig. 45 is a simple sliding switch in which
the base block has, at one end, a pair of copper
plates (A, B), each held at one end to the base
by a binding screw (C), and having a bearing or
contact surface (D) at its other end. At thep. 67
other end of the base is a copper plate (E) held
by a binding screw (F), to the inner end of which
plate is hinged a swinging switch blade (G), the
free end of which is adapted to engage with the
plates (A, B).

Fig. 45. Sliding Switch

Sliding Switch.—This sliding switch form may
have the contact plates (A, B and C, Fig. 46) circularly
arranged and any number may be located
on the base, so they may be engaged by a single
switching lever (H). It is the form usually
adopted for rheostats.

Reversing Switch.—A reversing switch is
shown in Fig. 47. The base has two plates (A, B)
at one end, to which the parallel switch bars
(C, D) are hinged. The other end of the base
has three contact plates (E, F, G) to engage thep. 68
swinging switch bars, these latter being at such
distance apart that they will engage with the
middle and one of the outer plates. The inlet
wires, positive and negative, are attached to the
plates (A, B, respectively), and one of the outlet
wires (H) is attached to the middle contact plate
(F), while the other wire is connected up with
both of the outside plates. When the switch bars
(C, D) are thrown to the left so as to be in contact
with E, F, the outside plate (E) and the middle
plate (F) will be positive and negative, respectively;
but when the switch is thrown to the
right, as shown in the figure, plate F becomes
positive and plate E negative, as shown.

Fig. 46. Rheostat Form of Switch

Push Buttons.—A push button is but a modified
structure of a switch, and they are serviceablep. 69
because they are operating, or the circuit is
formed only while the finger is on the button.

Fig. 47. Reversing Switch

In its simplest form (Fig. 48) the push button
has merely a circular base (A) of insulating material,
and near one margin, on the flat side, is a
rectangular plate (B), intended to serve as a
contact plate as well as a means for attaching
one of the wires thereto. In line with this plate
is a spring finger (C), bent upwardly so that it
is normally out of contact with the plate (B), its
end being held by a binding screw (D). To effect
contact, the spring end of the finger (C) is pressed
against the bar (B), as at E. This is enclosed
in a suitable casing, such as will readily suggest
itself to the novice.

Electric Bell.—One of the first things the boyp. 70
wants to make, and one which is also an interesting
piece of work, is an electric bell.

To make this he will be brought, experimentally,
in touch with several important features in electrical
work. He must make a battery for the
production of current, a pair of electro-magnets
to be acted upon by the current, a switch to control
it, and, finally, he must learn how to connect
it up so that it may be operated not only from
one, but from two or more push buttons.

Fig. 48. Push Button

How Made.—In Fig. 49 is shown an electric
bell, as usually constructed, so modified as to show
the structure at a glance, with its connections. A
is the base, B, B’ the binding posts for the wires,
C, C the electro-magnets, C’ the bracket for holding
the magnets, D the armature, E the thin
spring which connects the armature with the post
F, G the clapper arm, H the bell, I the adjusting
screw on the post J, K the wire lead from thep. 71
binding post B to the first magnet, L the wire
which connects the two magnets, M the wire which
runs from the second magnet to the post J, and
N a wire leading from the armature post to the
binding post B’.

Fig. 49. Electric Bell

The principle of the electric bell is this: In
looking at Fig. 49, you will note that the armature
bar D is held against the end of the adjustingp. 72
screw by the small spring E. When a current
is turned on, it passes through the connections
and conduits as follows: Wire K to the magnets,
wire M to the binding post J, and set screw I,
then through the armature to the post F, and
from post F to the binding post B’.

Fig. 50. Armature of Electric Bell

Electric Bell—How Operated.—The moment
a current passes through the magnets (C, C), the
core is magnetized, and the result is that the armature
(D) is attracted to the magnets, as shown
by the dotted lines (O), when the clapper strikes
the bell. But when the armature moves over to
the magnet, the connection is broken between the
screw (I) and armature (D), so that the cores
of the magnets are demagnetized and lose their
pull, and the spring (E) succeeds in drawingp. 73
back the armature. This operation of vibrating
the armature is repeated with great rapidity,
alternately breaking and re-establishing the circuit,
by the action of the current.

In making the bell, you must observe one thing,
the binding posts (B, B’) must be insulated from
each other, and the post J, or the post F, should
also be insulated from the base. For convenience
we show the post F insulated, so as to necessitate
the use of wire (N) from post (F) to binding post
(B’).

The foregoing assumes that you have used a
cast metal base, as most bells are now made;
but if you use a wooden base, the binding posts
(B, B’) and the posts (F, J) are insulated from
each other, and the construction is much simplified.

It is better, in practice, to have a small spring
(P, Fig. 50) between the armature (D) and the
end of the adjusting screw (I), so as to give a
return impetus to the clapper. The object of the
adjusting screw is to push and hold the armature
close up to the ends of the magnets, if it seems
necessary.

If two bells are placed on the base with the
clapper mounted between them, both bells will be
struck by the swinging motion of the armature.

An easily removable cap or cover is usuallyp. 74
placed over the coils and armature, to keep out
dust.

A very simple annunciator may be attached to
the bell, as shown in the following figures:

Figs. 51-54. Annunciator

Annunciators.—Make a box of wood, with a
base (A) 4″ × 5″ and ½ inch thick. On this you
can permanently mount the two side pieces (B)
and two top and bottom pieces (C), respectively,p. 75
so they project outwardly 4½ inches from the base.
On the open front place a wood or metal plate
(D), provided with a square opening (D), as in
Fig. 54, near its lower end. This plate is held
to the box by screws (E).

Within is a magnet (F), screwed into the base
(A), as shown in Fig. 51; and pivoted to the
bottom of the box is a vertical armature (G),
which extends upwardly and contacts with the
core of the magnet. The upper end of the armature
has a shoulder (H), which is in such position
that it serves as a rest for a V-shaped stirrup
(I), which is hinged at J to the base (C). This
stirrup carries the number plate (K), and when
it is raised to its highest point it is held on the
shoulder (H), unless the electro-magnet draws
the armature out of range of the stirrup. A
spring (L) bearing against the inner side of the
armature keeps its upper end normally away from
the magnet core. When the magnet draws the
armature inwardly, the number plate drops and
exposes the numeral through the opening in the
front of the box. In order to return the number
plate to its original position, as shown in Fig. 51,
a vertical trigger (M) passes up through the bottom,
its upper end being within range of one of
the limbs of the stirrup.

This is easily made by the ingenious boy, andp. 76
will be quite an acquisition to his stock of instruments.
In practice, the annunciator may be located
in any convenient place and wires run to
that point.

Fig. 55. Alarm Switch on Window

Fig. 56. Burglar Alarm Attachment to Window

Burglar Alarm.—In order to make a burglar
alarm connection with a bell, push buttons or
switches may be put in circuit to connect with thep. 77
windows and doors, and by means of the annunciators
you may locate the door or window which
has been opened. The simplest form of switch
for a window is shown in the following figures:

The base piece (A), which may be of hard rubber
or fiber, is ¼ inch thick and 1″ × 1½” in size.

Fig. 57. Burglar Alarm Contact

At one end is a brass plate (B), with a hole for a
wood screw (C), this screw being designed to pass
through the plate and also into the window-frame,
so as to serve as a means of attaching one of the
wires thereto. The inner end of the plate has a
hole for a round-headed screw (C’) that also goes
through the base and into the window-frame. It
also passes through the lower end of the heart-shaped
metal switch-piece (D)

p. 78

The upper end of the base has a brass plate
(E), also secured to the base and window by a
screw (F) at its upper end. The heart-shaped
switch is of such length and width at its upper
end that when it is swung to the right with one
of the lobes projecting past the edge of the window-frame,
the other lobe will be out of contact
with the plate (E).

Fig. 58. Neutral Position of Contact

The window sash (G) has a removable pin (H),
which, when the sash moves upwardly, is in the
path of the lobe of the heart-shaped switch, as
shown in Fig. 56, and in this manner the pin (H)
moves the upper end of the switch (D) inwardly,
so that the other lobe contacts with the plate (E),
and establishes an electric circuit, as shown in
Fig. 57. During the daytime the pin (H) may
be removed, and in order to protect the switchp. 79
the heart-shaped piece (D) is swung inwardly,
as shown in Fig. 58, so that neither of the lobes
is in contact with the plate (E).

Wire Circuiting.—For the purpose of understanding
fully the circuiting, diagrams will be
shown of the simple electric bell with two push
buttons; next in order, the circuiting with an
annunciator and then the circuiting necessary for
a series of windows and doors, with annunciator
attachments.

Fig. 59. Circuiting for Electric Bell

Circuiting System with a Bell and Two Push
Buttons.—Fig. 59 shows a simple circuiting system
which has two push buttons, although any
number may be used, so that the bell will ring
when the circuit is closed by either button.

The Push Buttons and the Annunciator
Bells.—Fig. 60 shows three push buttons and an
annunciator for each button. These three circuitsp. 80
are indicated by A, B and C, so that when
either button makes contact, a complete circuit is
formed through the corresponding annunciator.

Fig. 60. Annunciators

Fig. 61. Wiring System for a House

Wiring Up a House.—The system of wiring up
a house so that all doors and windows will be
connected to form a burglar alarm outfit, is shown
in Fig. 61. It will be understood that, in practice,
the bell is mounted on or at the annunciator, andp. 81
that, for convenience, the annunciator box has also
a receptacle for the battery. The circuiting is
shown diagramatically, as it is called, so as fully
to explain how the lines are run. Two windows
and a door are connected up with an annunciator
having three drops, or numbers 1, 2, 3. The circuit
runs from one pole of the battery to the bell
and then to one post of the annunciator. From
the other post a wire runs to one terminal of the
switch at the door or window. The other switch
terminal has a wire running to the other pole of
the battery.

A, B, C represent the circuit wires from the terminals
of the window and door switches, to the
annunciators.

It is entirely immaterial which side of the battery
is connected up with the bell.

From the foregoing it will readily be understood
how to connect up any ordinary apparatus,
remembering that in all cases the magnet must
be brought into the electric circuit.

p. 82

CHAPTER VIIIToC

ACCUMULATORS. STORAGE OR SECONDARY BATTERIES

Storing Up Electricity.—In the foregoing
chapters we have seen that, originally, electricity
was confined in a bottle, called the Leyden jar,
from which it was wholly discharged at a single
impulse, as soon as it was connected up by external
means. Later the primary battery and the
dynamo were invented to generate a constant
current, and after these came the second form
of storing electricity, called the storage or secondary
battery, and later still recognized as accumulators.

The Accumulator.—The term accumulator is,
strictly speaking, the more nearly correct, as electricity
is, in reality, “stored” in an accumulator.
But when an accumulator is charged by a current
of electricity, a chemical change is gradually produced
in the active element of which the accumulator
is made. This change or decomposition
continues so long as the charging current is on.
When the accumulator is disconnected from the
charging battery or dynamo, and its terminals
are connected up with a lighting system, or with
a motor, for instance, a reverse process is setp. 83
up, or the particles re-form themselves into their
original compositions, which causes a current to
flow in a direction opposite to that of the charging
current.

It is immaterial to the purposes of this chapter,
as to the charging source, whether it be by
batteries or dynamos; the same principles will
apply in either case.

Fig. 62. Accumulator Grids

Accumulator Plates.—The elements used for
accumulator plates are red lead for the positive
plates, and precipitated lead, or the well-known
litharge, for the negative plates. Experience has
shown that the best way to hold this material is
by means of lead grids

p. 84

Fig. 62 shows the typical form of one of these
grids. It is made of lead, cast or molded in one
piece, usually square, as at A, with a wing or
projection (B), at one margin, extending upwardly
and provided with a hole (C). The grid is
about a quarter of an inch thick.

The Grid.—The open space, called the grid,
proper, comprises cross bars, integral with the
plate, made in a variety of shapes. Fig. 62 shows
three forms of constructing these bars or ribs,
the object being to provide a form which will
hold in the lead paste, which is pressed in so
as to make a solid-looking plate when completed.

The Positive Plate.—The positive plate is made
in the following manner: Make a stiff paste of
red lead and sulphuric acid; using a solution, say,
of one part of acid to two parts of water. The
grid is laid on a flat surface and the paste forced
into the perforations with a stiff knife or spatula.
Turn over the grid so as to get the paste in evenly
on both sides.

The grid is then stood on its edge, from 18 to 20
hours, to dry, and afterwards immersed in a concentrated
solution of chloride of lime, so as to
convert it into lead peroxide. When the action
is complete it is thoroughly rinsed in cold water,
and is ready to use.

The Negative Plate.—The negative plate isp. 85
filled, in like manner, with precipitated lead. This
lead is made by putting a strip of zinc into a
standard solution of acetate of lead, and crystals
will then form on the zinc. These will be very
thin, and will adhere together, firmly, forming a
porous mass. This, when saturated and kept under
water for a short time, may be put into the
openings of the negative plate.

Fig. 63. Assemblage of Accumulator Plates

Connecting Up the Plates.—The next step is
to put these plates in position to form a battery.
In Fig. 63 is shown a collection of plates connected
together

p. 86

For simplicity in illustrating, the cell is made
up of glass, porcelain, or hard rubber, with five
plates (A), A, A representing the negative and B,
B the positive plates. A base of grooved strips
(C, C) is placed in the batteries of the cell to
receive the lower ends of the plates. The positive
plates are held apart by means of a short
section of tubing (D), which is clamped and held
within the plates by a bolt (E), this bolt also
being designed to hold the terminal strip (F).

In like manner, the negative plates are held
apart by the two tubular sections (G), each of
which is of the same length as the section D of
the positives. The bolt (H) holds the negatives
together as well as the terminal (I). The terminals
should be lead strips, and it would be well,
owing to the acid fumes which are formed, to
coat all brass work, screws, etc., with paraffine
wax.

The electrolyte or acid used in the cell, for
working purposes, is a pure sulphuric acid, which
should be diluted with about four times its weight
in water. Remember, you should always add the
strong acid to the water, and never pour the
water into the acid, as the latter method causes a
dangerous ebullition, and does not produce a good
mixture

p. 87

Put enough of this solution into the cell to cover
the tops of the plates, and the cell is ready.

Fig. 64. Connecting Up Storage Battery in Series

Charging the Cells.—The charge of the current
must never be less than 2.5 volts. Each cell
has an output, in voltage, of about 2 volts, hence
if we have, say, 10 cells, we must have at least
25 volts charging capacity. We may arrange
these in one line, or in series, as it is called, so
far as the connections are concerned, and charge
them with a dynamo, or other electrical source,
which shows a pressure of 25 volts, as illustrated
in Fig. 64, or, instead of this, we may put them
into two parallel sets of 5 cells each, as shown in
Fig. 65, and use 12.5 volts to charge with. In
this case it will take double the time because we
are charging with only one-half the voltage used
in the first case.

The positive pole of the dynamo should be
connected with the positive pole of the accumulatorp. 88
cell, and negative with negative. When
this has been done run up the machine until it
slightly exceeds the voltage of the cells. Thus,
if we have 50 cells in parallel, like in Fig. 64, at
least 125 volts will be required, and the excess
necessary should bring up the voltage in the dynamo
to 135 or 140 volts.

Fig. 65. Parallel Series

Fig. 66. Charging Circuit

The Initial Charge.—It is usual initially to
charge the battery from periods ranging from 36
to 40 hours, and to let it stand for 12 or 15 hours,
after which to re-charge, until the positive plates
have turned to a chocolate color, and the negativep. 89
plates to a slate or gray color, and both plates
give off large bubbles of gas.

In charging, the temperature of the electrolyte
should not exceed 100° Fahrenheit.

When using the accumulators they should never
be fully discharged.

The Charging Circuit.—The diagram (Fig.
66) shows how a charging circuit is formed. The
lamps are connected up in parallel, as illustrated.
Each 16-candle-power 105-volt lamp will carry ½
ampere, so that, supposing we have a dynamo
which gives 110 volts, and we want to charge a
4-volt accumulator, there will be 5-volt surplus to
go to the accumulator. If, for instance, you want
the cell to have a charge of 2 amperes, four of
these lamps should be connected up in parallel.
If 3 amperes are required, use 6 lamps, and so on.

p. 90

CHAPTER IXToC

THE TELEGRAPH

The telegraph is a very simple instrument.
The key is nothing more or less than a switch
which turns the current on and off alternately.

The signals sent over the wires are simply the
audible sounds made by the armature, as it moves
to and from the magnets.

Mechanism in Telegraph Circuits.—A telegraph
circuit requires three pieces of mechanism
at each station, namely, a key used by the sender,
a sounder for the receiver, and a battery.

The Sending Key.—The base of the sending instrument
is six inches long, four inches wide, and
three-quarters of an inch thick, made of wood,
or any suitable non-conducting material. The key
(A) is a piece of brass three-eighths by one-half
inch in thickness and six inches long. Midway
between its ends is a cross hole, to receive the
pivot pin (B), which also passes through a pair
of metal brackets (C, D), the bracket C having
a screw to hold one of the line wires, and the other
bracket having a metal switch (E) hinged thereto.
This switch bar, like the brackets, is made ofp. 91
brass, one-half inch wide by one-sixteenth of an
inch thick.

Below the forward end of the key (A) is a cross
bar of brass (F), screwed to the base by a screw
at one end, to receive the other line wire. Directly
below the key (A) is a screw (G), so that the key
will strike it when moved downwardly. The other
end of the bar (F) contacts with the forward end
of the switch bar (E) when the latter is moved
inwardly.

Fig. 67. Telegraph Sending Key

The forward end of the key (A) has a knob
(H) for the fingers, and the rear end has an
elastic (I) attached thereto which is secured to
the end of the base, so that, normally, the rear
end is held against the base and away from the
screw head (G). The head (J) of a screw projects
from the base at its rear end. Key A contacts
with it.

When the key A contacts with the screw headsp. 92
G, J, a click is produced, one when the key is
pressed down and the other when the key is released.

You will notice that the two plates C, F are
connected up in circuit with the battery, so that,
as the switch E is thrown, so as to be out of contact,
the circuit is open, and may be closed either
by the key A or the switch E. The use of the
switch will be illustrated in connection with the
sounder.

Fig. 68. Telegraph Sounder

When the key A is depressed, the circuit of
course goes through plate C, key A and plate
F to the station signalled.

The Sounder.—The sounder is the instrument
which carries the electro-magnet.

In Fig. 68 this is shown in perspective. The
base is six inches long and four inches wide, beingp. 93
made, preferably, of wood. Near the forward
end is mounted a pair of electro-magnets (A, A),
with their terminal wires connected up with plates
B, B’, to which the line wires are attached.

Midway between the magnets and the rear end
of the base is a pair of upwardly projecting brackets
(C). Between these are pivoted a bar (D),
the forward end of which rests between the magnets
and carries, thereon, a cross bar (E) which
is directly above the magnets, and serves as the
armature.

The rear end of the base has a screw (F) directly
beneath the bar D of such height that when
the rear end of the bar D is in contact therewith
the armature E will be out of contact with the
magnet cores (A, A). A spiral spring (G) secured
to the rear ends of the arm and to the base,
respectively, serves to keep the rear end of the
key normally in contact with the screw F.

Connecting Up the Key and Sounder.—Having
made these two instruments, we must next
connect them up in the circuit, or circuits, formed
for them, as there must be a battery, a key, and
a sounder at each end of the line.

In Fig. 69 you will note two groups of those
instruments. Now observe how the wires connect
them together. There are two line wires, one
(A) which connects up the two batteries, the wirep. 94
being attached so that one end connects with the
positive terminal of the battery, and the other end
with the negative terminal.

Fig. 69. A Telegraph Circuit

The other line wire (B), between the two stations,
has its opposite ends connected with the
terminals of the electro-magnet C of the sounders.
The other terminals of each electro-magnet are
connected up with one terminal of each key by a
wire (D), and to complete the circuit at each
station, the other terminal of the key has a wire
(E) to its own battery.

Two Stations in Circuit.—The illustration
shows station 2 telegraphing to station 1. This
is indicated by the fact that the switch F’ of
that instrument is open, and the switch F of
station 1 closed. When, therefore, the key of
station 2 is depressed, a complete circuit is formedp. 95
which transmits the current through wire E’ and
battery, through line A, then through the battery
of station 1, through wire E to the key, and from
the key, through wire D, to the sounder, and
finally from the sounder over line wire B back
to the sounder of station 2, completing the circuit
at the key through wire D’.

When the operator at station 2 closes the switch
F’, and the operator at station 1 opens the switch
F, the reverse operation takes place. In both
cases, however, the sounder is in at both ends
of the line, and only the circuit through the key
is cut out by the switch F, or F’.

The Double Click.—The importance of the
double click of the sounder will be understood
when it is realized that the receiving operator
must have some means of determining if the
sounder has transmitted a dot or a dash. Whether
he depresses the key for a dot or a dash, there
must be one click when the key is pressed down
on the screw head G (Fig. 62), and also another
click, of a different kind, when the key is raised
up so that its rear end strikes the screw head J.
This action of the key is instantly duplicated by
the bar D (Fig. 68) of the sounder, so that the
sounder as well as the receiver knows the time
between the first and the second click, and by that
means he learns that a dot or a dash is made

p. 96

Illustrating the Dot and the Dash.—To illustrate:
Let us suppose, for convenience, that the
downward movement of the lever in the key, and
the bar in the sounder, make a sharp click, and
the return of the lever and bar make a dull click.
In this case the ear, after a little practice, can
learn readily how to distinguish the number of
downward impulses that have been given to the
key.

The Morse Telegraph Code

Example in Use.—Let us take an example in
the word “electrical.”

p. 97

The operator first makes a dot, which means
a sharp and a dull click close together; there is
then a brief interval, then a lapse, after which
there is a sharp click, followed, after a comparatively
longer interval, with the dull click. Now
a dash by itself may be an L, a T, or the figure
0, dependent upon its length. The short dash
is T, and the longest dash the figure 0. The operator
will soon learn whether it is either of these
or the letter L, which is intermediate in length.

In time the sender as well as receiver will
give a uniform length to the dash impulse, so
that it may be readily distinguished. In the same
way, we find that R, which is indicated by a dot,
is followed, after a short interval, by two dots.
This might readily be mistaken for the single dot
for E and the two dots for I, were it not that
the time element in R is not as long between the
first and second dots, as it ordinarily is between
the single dot of E when followed by the two
dots of I.

p. 98

CHAPTER XToC

HIGH TENSION APPARATUS, CONDENSERS, ETC.

Induction.—One of the most remarkable things
in electricity is the action of induction—that property
of an electric current which enables it to
pass from one conductor to another conductor
through the air. Another singular and interesting
thing is that the current so transmitted across
spaces changes its direction of flow, and, furthermore,
the tension of such a current may be
changed by transmitting it from one conductor to
another.

Low and High Tension.—In order to effect this
latter change—that is, to convert it from a low
tension to a high tension—coils are used, one coil
being wound upon the other; one of these coils is
called the primary and the other the secondary.
The primary coil receives the current from the
battery, or source of electrical power, and the secondary
coil receives charges, and transmits the
current.

For an illustration of this examine Fig. 70, in
which you will note a coil of heavy wire (A),
around which is wound a coil of fine wire (B).
If, for instance, the primary coil has a low voltage,p. 99
the secondary coil will have a high voltage,
or tension. Advantage is taken of this phase to
use a few cells, as a primary battery, and then,
by a set of Induction Coils, as they are called,
to build up a high-tension electro-motive force,
so that the spark will jump across a gap, as shown
at C, for the purpose of igniting the charges of
gas in a gasoline motor; or the current may be
used for medical batteries, and for other purposes.

Fig. 70. Induction Coil and Circuit

The current passes, by induction, from the primary
to the secondary coil. It passes from a
large conductor to a small conductor, the small
conductor having a much greater resistance than
the large one.

Elastic Property of Electricity.—While electricity
has no resiliency, like a spring, for instance,
still it acts in the manner of a cushion
under certain conditions. It may be likened to an
oscillating spring acted upon by a bar

p. 100

Referring to Fig. 71, we will assume that the
bar A in falling down upon the spring B compresses
the latter, so that at the time of greatest
compression the bar goes down as far as the
dotted line C. It is obvious that the spring B
will throw the bar upwardly. Now, electricity
appears to have a kind of elasticity, which characteristic
is taken advantage of in order to increase
the efficiency of the induction in the coil.

Fig. 71. Illustrating Elasticity

The Condenser.—To make a condenser, prepare
two pine boards like A, say, eight by ten
inches and a half inch thick, and shellac thoroughly
on all sides. Then prepare sheets of tinfoil
(B), six by eight inches in size, and also sheets
of paraffined paper (C), seven by nine inches in
dimensions. Also cut out from the waste pieces
of tinfoil strips (D), one inch by two inches.
To build up the condenser, lay down a sheet of
paraffined paper (C), then a sheet of tinfoil (B),p. 101
and before putting on the next sheet of paraffined
paper lay down one of the small strips (D) of
tinfoil, as shown in the illustration, so that its
end projects over one end of the board A; then
on the second sheet of paraffine paper lay another
sheet of tinfoil, and on this, at the opposite
end, place one of the small strips (D), and so
on, using from 50 to 100 of the tinfoil sheets.
When the last paraffine sheet is laid on, the other
board is placed on top, and the whole bound together,
either by wrapping cords around the same
or by clamping them together with bolts.

Fig. 72. Condenser

You may now make a hole through the projecting
ends of the strips, and you will have two
sets of tinfoil sheets, alternately connected together
at opposite ends of the condenser.

Care should be exercised to leave the paraffine
sheets perfect or without holes. You can makep. 102
these sheets yourself by soaking them in melted
paraffine wax.

Connecting Up a Condenser.—When completed,
one end of the condenser is connected
up with one terminal of the secondary coil, and
the other end of the condenser with the other
secondary terminal.

Fig. 73. High-tension Circuit

In Fig. 73 a high-tension circuit is shown. Two
coils, side by side, are always used to show an
induction coil, and a condenser is generally shown,
as illustrated, by means of a pair of forks, one
resting within the other.

The Interrupter.—One other piece of mechanism
is necessary, and that is an Interrupter,
for the purpose of getting the effect of the pulsations
given out by the secondary coil.

A simple current interrupter is made as follows:
Prepare a wooden base (A), one inch
thick, six inches wide, and twelve inches long.
Upon this mount a toothed wheel (B), six inchesp. 103
in diameter, of thin sheet metal, or a brass gear
wheel will answer the purpose. The standard
(C), which supports the wheel, may be of metal
bent up to form two posts, between which the
crankshaft (D) is journaled. The base of the
posts has an extension plate (E), with a binding
post for a wire. At the front end of the base is an
L-shaped strip (F), with a binding post for a
wire connection, and the upwardly projecting
part of the strip contacts with the toothed wheel.
When the wheel B is rotated the spring finger (F)
snaps from one tooth to the next, so that, momentarily,
the current is broken, and the frequency
is dependent upon the speed imparted to
the wheel.

Fig. 74. Current Interrupter

Uses of High-tension Coils.—This high-tension
coil is made use of, and is the essential apparatus
in wireless telegraphy, as we shall see in
the chapter treating upon that subject.

p. 104

CHAPTER XIToC

WIRELESS TELEGRAPHY

Telegraphing Without Wires.—Wireless telegraphy
is an outgrowth of the ordinary telegraph
system. When Maxwell, and, later on,
Hertz, discovered that electricity, magnetism, and
light were transmitted through the ether, and
that they differed only in their wave lengths, they
laid the foundations for wireless telegraphy.
Ether is a substance which is millions and millions
of times lighter than air, and it pervades
all space. It is so unstable that it is constantly
in motion, and this phase led some one to suggest
that if a proper electrical apparatus could be
made, the ether would thereby be disturbed sufficiently
so that its impulses would extend out a
distance proportioned to the intensity of the electrical
agitation thereby created.

Surging Character of High-tension Currents.—When
a current of electricity is sent through
a wire, hundreds of miles in length, the current
surges back and forth on the wire many thousands
of times a second. Light comes to us from
the sun, over 90,000,000 of miles, through the
ether. It is as reasonable to suppose, or infer,p. 105
that the ether can, therefore, convey an electrical
impulse as readily as does a wire.

It is on this principle that impulses are sent
for thousands of miles, and no doubt they extend
even farther, if the proper mechanism could be
devised to detect movement of the waves so propagated.

The Coherer.—The instrument for detecting
these impulses, or disturbances, in the ether is
generally called a coherer, although detector is
the term which is most satisfactory. The name
coherer comes from the first practical instrument
made for this purpose.

Fig. 75. Wireless Telegraphy Coherer

How Made.—The coherer is simply a tube, say,
of glass, within which is placed iron filings. When
the oscillations surge through the secondary coil
the pressure or potentiality of the current finally
causes it to leap across the small space separating
the filings and, as it were, it welds together
their edges so that a current freely passes. Thep. 106
bringing together of the particles, under these
conditions, is called cohering.

Fig. 75 shows the simplest form of coherer. The
posts (A) are firmly affixed to the base (B), each
post having an adjusting screw (C) in its upper
end, and these screw downwardly against and
serve to bind a pair of horizontal rods (D), the
inner ends of which closely approach each other.
These may be adjusted so as to be as near together
or as far apart as desired. E is a glass
tube in which the ends of the rods (D) rest, and
between the separated ends of the rods (D) the
iron filings (F) are placed.

The Decoherers.—For the purpose of causing
the metal filings to fall apart, or decohere,
the tube is tapped lightly, and this is done by a
little object like the clapper of an electric bell.

In practice, the coils and the parts directly connected
with it are put together on one base.

The Sending Apparatus.—Fig. 76 shows a section
of a coil with its connection in the sending
station. The spark gap rods (A) may be swung
so as to bring them closer together or farther
apart, but they must not at any time contact
with each other.

The induction coil has one terminal of the primary
coil connected up by a wire (B) with one
post of a telegraph key, and the other post ofp. 107
the key has a wire connection (C), with one side
of a storage battery. The other side of the battery
has a wire (D) running to the other terminal
of the primary.

Fig. 76. Wireless Sending Apparatus

The secondary coil has one of its terminals
connected with a binding post (E). This binding
post has an adjustable rod with a knob (F) on
its end, and the other binding post (G), which
is connected up with the other terminal of thep. 108
secondary coil, carries a similar adjusting rod
with a knob (H).

From the post (E) is a wire (I), which extends
upwardly, and is called the aerial wire, or wire
for the antennæ, and this wire also connects with
one side of the condenser by a conductor (J).
The ground wire (K) connects with the other
binding post (G), and a branch wire (L) also
connects the ground wire (K) with one end of the
condenser.

Fig. 77. Wireless Receiving Apparatus

The Receiving Apparatus.—The receiving station,
on the other hand, has neither condenser, induction
coil, nor key. When the apparatus is in
operation, the coherer switch is closed, and the
instant a current passes through the coherer and
operates the telegraph sounder, the galvanometer
indicates the current.

Of course, when the coherer switch is closed,
the battery operates the decoherer

p. 109

How the Circuits are Formed.—By referring
again to Fig. 76, it will be seen that when the
key is depressed, a circuit is formed from the battery
through wire B to the primary coil, and back
again to the battery through wire D. The secondary
coil is thereby energized, and, when the
full potential is reached, the current leaps across
the gap formed between the two knobs (F, H),
thereby setting up a disturbance in the ether
which is transmitted through space in all directions.

It is this impulse, or disturbance, which is received
by the coherer at the receiving station,
and which is indicated by the telegraph sounder.

p. 110

CHAPTER XIIToC

THE TELEPHONE

Vibrations.—Every manifestation in nature is
by way of vibration. The beating of the heart,
the action of the legs in walking, the winking of
the eyelid; the impulses from the sun, which we
call light; sound, taste and color appeal to our
senses by vibratory means, and, as we have hereinbefore
stated, the manifestations of electricity
and magnetism are merely vibrations of different
wave lengths.

The Acoustic Telephone.—That sound is
merely a product of vibrations may be proven in
many ways. One of the earliest forms of telephones
was simply a “sound” telephone, called
the Acoustic Telephone. The principle of this
may be illustrated as follows:

Take two cups (A, B), as in Fig. 78, punch a
small hole through the bottom of each, and run a
string or wire (C) from the hole of one cup to
that of the other, and secure it at both ends so
it may be drawn taut. Now, by talking into the
cup (A) the bottom of it will vibrate to and
fro, as shown by the dotted lines and thereby
cause the bottom of the other cup (B) to vibratep. 111
in like manner, and in so vibrating it will receive
not only the same amplitude, but also the same
character of vibrations as the cup (A) gave forth.

Fig. 78. Acoustic Telephone

Fig. 79. Illustrating Vibrations

Sound Waves.—Sound waves are long and
short; the long waves giving sounds which are
low in the musical scale, and the short waves high
musical tones. You may easily determine this by
the following experiment:

Stretch a wire, as at B (Fig. 79), fairly tight,
and then vibrate it. The amplitude of the vibration
will be as indicated by dotted line A. Now,
stretch it very tight, as at C, so that the amplitude
of vibration will be as shown at E. By putting
your ear close to the string you will find that while
A has a low pitch, C is very much higher. Thisp. 112
is the principle on which stringed instruments are
built. You will note that the wave length, which
represents the distance between the dotted lines
A is much greater than E.

Hearing Electricity.—In electricity, mechanism
has been made to enable man to note the action
of the current. By means of the armature,
vibrating in front of a magnet, we can see its
manifestations. It is now but a step to devise
some means whereby we may hear it. In this,
as in everything else electrically, the magnet
comes into play.

Fig. 80. The Magnetic Field

In the chapter on magnetism, it was stated that
the magnetic field extended out beyond the magnet,
so that if we were able to see the magnetism,
the end of a magnet would appear to us something
like a moving field, represented by the dotted lines
in Fig. 80.

The magnetic field is shown in Fig. 80 at onlyp. 113
one end, but its manifestations are alike at both
ends. It will be seen that the magnetic field extends
out to a considerable distance and has quite
a radius of influence.

The Diaphragm in a Magnetic Field.—If, now,
we put a diaphragm (A) in this magnetic field,
close up to the end of the magnet, but not so
close as to touch it, and then push it in and out,
or talk into it so that the sound waves strike it,
the movement or the vibration of the diaphragm
(A) will disturb the magnetic field emanating
from the magnet, and this disturbance of the magnetic
field at one end of the magnet also affects
the magnetic field at the other end in the same
way, so that the disturbance there will be of the
same amplitude. It will also display the same
characteristics as did the magnetic field when the
diaphragm (A) disturbed it.

A Simple Telephone Circuit.—From this simple
fact grew the telephone. If two magnets are
connected up in the same circuit, so that the magnetic
fields of the two magnets have the same
source of electric power, the disturbance of one
diaphragm will affect the other similarly, just the
same as the two magnetic fields of the single
magnet are disturbed in unison.

How to Make a Telephone.—For experimental
and testing purposes two of these telephonesp. 114
should be made at the same time. The case or
holder (A) may be made either of hard wood or
hard rubber, so that it is of insulating material.
The core (B) is of soft iron, ⅜ inch in diameter
and 5 inches long, bored and threaded at one end
to receive a screw (C) which passes through the
end of the case (A).

The enlarged end of the case should be, exteriorly,
2¼ inches in diameter, and the body of the
case 1 inch in diameter.

Fig. 81. Section of Telephone Receiver

Interiorly, the large end of the case is provided
with a circular recess 1¾ inches in diameter and
adapted to receive therein a spool which is,
diametrically, a little smaller than the recess. The
spool fits fairly tight upon the end of the core,
and when in position rests against an annular
shoulder in the recess. A hollow space (F) is thus
provided behind the spool (D), so the two wiresp. 115
from the magnet may have room where they
emerge from the spool.

The spool is a little shorter than the distance
between the shoulder (E) and the end of the casing,
at G, and the core projects only a short distance
beyond the end of the spool, so that when
the diaphragm (H) is put upon the end of the
case, and held there by screws (I) it will not
touch the end of the core. A wooden or rubber
mouthpiece (J) is then turned up to fit over the
end of the case.

Fig. 82. The Magnet and Receiver Head

The spool (D) is made of hard rubber, and is
wound with No. 24 silk-covered wire, the windings
to be well insulated from each other. The
two ends of the wire are brought out, and threaded
through holes (K) drilled longitudinally through
the walls of the case, and affixed to the end by
means of screws (L), so that the two wires may be
brought together and connected with a duplex
wire (M)

p. 116

As the screw (C), which holds the core in place,
has its head hidden within a recess, which can be
closed up by wax, the two terminals of the wires
are well separated so that short-circuiting cannot
take place.

Telephone Connections.—The simplest form
of telephone connection is shown in Fig. 83. This
has merely the two telephones (A and B), with a
single battery (C) to supply electricity for both.
One line wire (D) connects the two telephones
directly, while the other line (E) has the battery
in its circuit.

Fig. 83. Simple Telephone Connection

Complete Installation.—To install a more
complete system requires, at each end, a switch,
a battery and an electro-magneto bell. You may
use, for this purpose, a bell, made as shown in
the chapter on bells.

Fig. 84 shows such a circuit. We now dispense
with one of the line wires, because it has been
found that the ground between the two stations
serves as a conductor, so that only one line wire
(A) is necessary to connect directly with the telephonesp. 117
of the two stations. The telephones
(B, B’, respectively) have wires (C, C’) running
to the pivots of double-throw switches (D, D’),
one terminal of the switches having wires (E, E’),
which go to electric bells (F, F’), and from the
bells are other wires (G, G’), which go to the
ground. The ground wires also have wires (H,
H’), which go to the other terminals of the switch
(D, D’). The double-throw switch (D, D’), in the
two stations, is thrown over so the current, if
any should pass through, will go through the bell
to the ground, through the wires (E, G or E’, G’).

Fig. 84. Telephone Stations in Circuit

Now, supposing the switch (D’), in station 2,
should be thrown over so it contacts with the wire
(H’). It is obvious that the current will then
flow from the battery (I’) through wires (H’, C’)
and line (A) to station 1; then through wire
C, switch D, wire E to the bell F, to the
ground through wire G. From wire G the current
returns through the ground to station 2,p. 118
where it flows up wire G’ to the battery, thereby
completing the circuit.

Fig. 85. Illustrating Light Contact Points

The operator at station 2, having given the
signal, again throws his switch (D’) back to the
position shown in Fig. 84, and the operator at
station 1 throws on his switch (D), so as to ring
the bell in station 2, thereby answering the signal,
which means that both switches are again to be
thrown over so they contact with the battery wires
(H and H’), respectively. When both are thus
thrown over, the bells (G, G’) are cut out of the
circuit, and the batteries are both thrown in, so
that the telephones are now ready for talking purposes.

Microphone.—Originally this form of telephone
system was generally employed, but it was found
that for long distances a more sensitive instrument
was necessary.

Light Contact Points.—In 1877 Professor
Hughes discovered, accidentally, that a light contact
point in an electric circuit augmented the
sound in a telephone circuit. If, for instance, ap. 119
light pin, or a nail (A, Fig. 85) should be used
to connect the severed ends of a wire (B), the
sounds in the telephone not only would be louder,
but they would be more distinct, and the first instrument
made practically, to demonstrate this, is
shown in Fig. 86.

Fig. 86. Microphone	Fig. 87. Transmitter

How to Make a Microphone.—This instrument
has simply a base (A) of wood, and near one end
is a perpendicular sounding-board (B) of wood,
to one side of which is attached, by wax or otherwise,
a pair of carbon blocks (C, D). The lower
carbon block (C) has a cup-shaped depression in
its upper side, and the upper block has a similar
depression in its lower side. A carbon pencil
(E) is lightly held within these cups, so that the
lightest contact of the upper end of the pencilp. 120
with the carbon block, makes the instrument so
sensitive that a fly, walking upon the sounding-board,
may be distinctly heard through the telephone
which is in the circuit.

Microphone the Father of the Transmitter.—This
instrument has been greatly modified, and
is now used as a transmitter, the latter thereby
taking the place of the pin (A), shown in Fig. 85.

Automatic Cut-outs for Telephones.—In the
operation of the telephone, the great drawback
originally was in inducing users of the lines to
replace or adjust their instruments carefully.
When switches were used, they would forget to
throw them back, and all sorts of trouble resulted.

It was found necessary to provide an automatic
means for throwing in and cutting out an instrument,
this being done by hanging the telephone
on the hook, so that the act merely of leaving the
telephone made it necessary, in replacing the instrument,
to cut out the apparatus.

Before describing the circuiting required for
these improvements, we show, in Fig. 87, a section
of a transmitter.

A cup-shaped case (A) is provided, made of
some insulating material, which has a diaphragm
(B) secured at its open side. This diaphragm
carries the carbon pencil (C) on one side and
from the blocks which support the carbon pencilp. 121
the wires run to binding posts on the case. Of
course the carbon supporting posts must be insulated
from each other, so the current will go
through the carbon pencil (C).

Complete Circuiting with Transmitter.—In
showing the circuiting (Fig. 88) it will not be possible
to illustrate the boxes, or casings, which receive
the various instruments. For instance, the
hook which carries the telephone or the receiver,
is hinged within the transmitter box. The circuiting
is all that it is intended to show.

Fig. 88. Complete Telephonic Circuit

The batteries of the two stations are connected
up by a wire (A), unless a ground circuit is used.
The other side of each battery has a wire connection
(B, B’) with one terminal of the transmitter,
and the other terminal of the transmitter has a
wire (C, C’) which goes to the receiver. From
the other terminal of the receiver is a wire (D, D’)
which leads to the upper stop contact (E, E’) ofp. 122
the telephone hook. A wire (F, F’) from the
lower stop contact (G, G’) of the hook goes to one
terminal of the bell, and from the other terminal
of the bell is a wire (H, H’) which makes connection
with the line wire (A). In order to make a
complete circuit between the two stations, a line
wire (I) is run from the pivot of the hook in station
1 to the pivot of the hook in station 2.

In the diagram, it is assumed that the receivers
are on the hooks, and that both hooks are, therefore,
in circuit with the lower contacts (G, G’), so
that the transmitter and receiver are both out of
circuit with the batteries, and the bell in circuit;
but the moment the receiver, for instance, in station
1 is taken off the hook, the latter springs up
so that it contacts with the stop (E), thus establishing
a circuit through the line wire (I) to the
hook of station 2, and from the hook through line
(F’) to the bell. From the bell, the line (A) carries
the current back to the battery of station (A),
thence through the wire (B) to the transmitter
wire (C) to receiver and wire (D) to the post (E),
thereby completing the circuit.

When, at station 2, the receiver is taken off the
hook, and the latter contacts with the post (E’),
the transmitter and receiver of both stations are
in circuit with each other, but both bells are cut
out.

p. 123

CHAPTER XIIIToC

ELECTROLYSIS, WATER PURIFICATION, ELECTROPLATING

Decomposing Liquids.—During the earlier experiments
in the field of electricity, after the battery
or cell was discovered, it was noted that
when a current was formed in the cell, the electrolyte
was charged and gases evolved from it. A
similar action takes place when a current of electricity
passes through a liquid, with the result
that the liquid is decomposed—that is, the liquid
is broken up into its original compounds. Thus,
water is composed of two parts, by bulk, of hydrogen
and of oxygen, so that if two electrodes are
placed in water, and a current is sent through the
electrodes in either direction, all the water will
finally disappear in the form of hydrogen and oxygen
gases.

Making Hydrogen and Oxygen.—During this
electrical action, the hydrogen is set free at the
negative pole and the oxygen at the positive pole.
A simple apparatus, which any boy can make, to
generate pure oxygen and pure hydrogen, is
shown in Fig. 89.

It is constructed of a glass or earthen jar (A),
preferably square, to which is fitted a wooden topp. 124
(B), this top being provided with a packing ring
(C), so as to make it air-tight. Within is a vertical
partition (D), the edges of which, below the
cap, fit tightly against the inner walls of the jar.
This partition extends down into the jar a sufficient
distance so it will terminate below the water
level. A pipe is fitted through the top on each
side of the partition, and each pipe has a valve.
An electrode, of any convenient metal, is secured
at its upper end to the top of the cap, on each side
of the partition. These electrodes extend down
to the bottom of the jar, and an electric wire connects
with each of them at the top.

Fig. 89. Device for Making Hydrogen and Oxygen

If a current of electricity is passed through the
wires and the electrodes, in the direction shownp. 125
by the darts, hydrogen will form at the negative
pole, and oxygen at the positive pole. These
gases will escape upwardly, so that they will be
trapped in their respective compartments, and
may be drawn off by means of the pipes.

Purifying Water.—Advantage is taken of this
electrolytic action, to purify water. Oxygen is
the most wonderful chemical in nature. It is
called the acid-maker of the universe. The name
is derived from two words, oxy and gen; one denoting
oxydation, and the other that it generates.
In other words, it is the generator of oxides. It
is the element which, when united with any other
element, produces an acid, an alkali or a neutral
compound.

Rust.—For instance, iron is largely composed
of ferric acid. When oxygen, in a free or gaseous
state, comes into contact with iron, it produces
ferrous oxide, which is recognized as rust.

Oxygen as a Purifier.—But oxygen is also a
purifier. All low forms of animal life, like bacteria
or germs in water, succumb to free oxygen.
By free oxygen is meant oxygen in the form of
gas.

Composition of Water.—Now, water, in which
harmful germs live, is one-third oxygen. Nevertheless,
the germs thrive in water, because the
oxygen is in a compound state, and, therefore, notp. 126
an active agent. But if oxygen, in the form of
gas, can be forced through water, it will attack the
germs, and destroy them.

Common Air Not a Good Purifier.—Water may
be purified, to a certain extent, by forcing common
air through it, and the foulest water, if run
over rocks, will be purified, in a measure, because
air is intermingled with it. But common air is
composed of four-fifths nitrogen, and only one-fifth
oxygen, and, as nitrogen is the staple article
of food for bacteria, the purifying method by air
is not effectual.

Pure Oxygen.—When, however, oxygen is generated
from water, by means of electrolysis, it is
pure; hence is more active and is not tainted by a
life-giving substance for germs, such as nitrogen.

The mechanism usually employed for purifying
water is shown in Fig. 90.

A Water Purifier.—The case (A, Fig. 90) may
be made of metal or of an insulating material.
If made of metal it must be insulated within with
slate, glass, marble or hard rubber, as shown at
B. The case is provided with exterior flanges
(C, D), with upper and lower ends, and it is
mounted upon a base plate (E) and affixed thereto
by bolts. The upper end has a conically-formed
cap (F) bolted to the flanges (C), and this has
an outlet to which a pipe (G) is attached. Thep. 127
water inlet pipe (H) passes through the lower
end of the case (A). The electrodes (I, J) are
secured, vertically, within the case, separated
from each other equidistant, each alternate electrode
being connected up with one wire (K), and
the alternate electrodes with a wire (L).

Fig. 90. Electric Water Purifier

p. 128

When the water passes upwardly, the decomposed
or gaseous oxygen percolates through the
water and thus attacks the germs and destroys
them.

The Use of Hydrogen in Purification.—On
the other hand, the hydrogen also plays an important
part in purifying the water. This depends
upon the material of which the electrodes are
made. Aluminum is by far the best material, as
it is one of nature’s most active purifiers. All
clay contains aluminum, in what is known as the
sulphate form, and water passing through the
clay of the earth thereby becomes purified, because
of this element.

Aluminum Electrodes.—When this material is
used as the electrodes in water, hydrate of aluminum
is formed, or a compound of hydrogen and
oxygen with aluminum. The product of decomposition
is a flocculent matter which moves upwardly
through the water, giving it a milky appearance.
This substance is like gelatine, so that
it entangles or enmeshes the germ life and prevents
it from passing through a filter.

If no filter is used, this flocculent matter, as
soon as it has given off the gases, will settle to
the bottom and carry with it all decomposed matter,
such as germs and other organic matter attackedp. 129
by the oxygen, which has become entangled
in the aluminum hydrate.

Electric Hand Purifier.—An interesting and
serviceable little purifier may be made by any
boy with the simplest tools, by cutting out three
pieces of sheet aluminum. Hard rolled is best
for the purpose. It is better to have one of the
sheets (A), the middle one, thicker than the two
outer plates (B).

Fig. 91. Portable Electric Purifier

Let each sheet be 1½ inches wide and 5½ inches
thick. One-half inch from the upper ends of thep. 130
two outside plates (B, B) bore bolt holes (C), each
of these holes being a quarter of an inch from
the edge of the plate. The inside plate (A) has
two large holes (D) corresponding with the small
holes (C) in the outside plates. At the upper
end of this plate form a wing (E), ½ inch wide
and ½ inch long, provided with a small hole for a
bolt. Next cut out two hard-rubber blocks (F),
each 1½ inches long, 1 inch wide and ⅜ inch thick,
and then bore a hole (G) through each, corresponding
with the small holes (C) in the plates
(B). The machine is now ready to be assembled.
If the inner plate is ⅛ inch thick and the outer
plates each 1/16 inch thick, use two small eighth-inchp. 131
bolts 1¼ inches long, and clamp together the
three plates with these bolts. One of the bolts may
be used to attach thereto one of the electric wires
(H), and the other wire (I) is attached by a bolt
to the wing (E).

Figs. 92-95. Details of Portable Purifier

Such a device will answer for a 110-volt circuit,
in ordinary water. Now fill a glass nearly full
of water, and stand the purifier in the glass.
Within a few minutes the action of electrolysis
will be apparent by the formation of numerous
bubbles on the plates, followed by the decomposition
of the organic matter in the water. At first
the flocculent decomposed matter will rise to the
surface of the water, but before many minutes it
will settle to the bottom of the glass and leave
clear water above.

Purification and Separation of Metals.—This
electrolytic action is utilized in metallurgy for the
purpose of producing pure metals, but it is more
largely used to separate copper from its base.
In order to utilize a current for this purpose, a
high ampere flow and low voltage are required.
The sheets of copper, containing all of its impurities,
are placed within a tank, parallel with a thin
copper sheet. The impure sheet is connected with
the positive pole of an electroplating dynamo, and
the thin sheet of copper is connected with the
negative pole. The electrolyte in the tank is ap. 132
solution of sulphate of copper. The action of
the current will cause the pure copper in the impure
sheet to disintegrate and it is then carried
over and deposited upon the thin sheet, this action
continuing until the impure sheet is entirely eaten
away. All the impurities which were in the sheet
fall to the bottom of the tank.

Other metals are treated in the same way, and
this treatment has a very wide range of usefulness.

Electroplating.—The next feature to be considered
in electrolysis is a most interesting and
useful one, because a cheap or inferior metal may
be coated by a more expensive metal. Silver and
nickel plating are brought about by this action of
a current passing through metals, which are immersed
in an electrolyte.

Plating Iron with Copper.—We have room in
this chapter for only one concrete example of
this work, which, with suitable modifications, is
an example of the art as practiced commercially.
Iron, to a considerable extent, is now being coated
with copper to preserve it from rust. To carry
out this work, however, an electroplating dynamo,
of large amperage, is required, the amperage, of
course, depending upon the surface to be treated
at one time. The pressure should not exceed 5
volts

p. 133

The iron surface to be treated should first be
thoroughly cleansed, and then immediately put
into a tank containing a cyanide of copper solution.
Two forms of copper solution are used, namely,
the cyanide, which is a salt solution of copper,
and the sulphate, which is an acid solution of
copper. Cyanide is first used because it does not
attack the iron, as would be the case if the sulphate
solution should first come into contact with
the iron.

A sheet of copper, termed the anode, is then
placed within the tank, parallel with the surface
to be plated, known as the cathode, and so
mounted that it may be adjusted to or from the
iron surface, or cathode. A direct current of
electricity is then caused to flow through the copper
plate and into the iron plate or surface, and
the plating proceeded with until the iron surface
has a thin film of copper deposited thereon. This
is a slow process with the cyanide solution, so
it is discontinued as soon as possible, after the
iron surface has been completely covered with
copper. This copper surface is thoroughly
cleaned off to remove therefrom the saline or alkaline
solution, and it is then immersed within a
bath, containing a solution of sulphate of copper.
The current is then thrown on and allowed sop. 134
to remain until it has deposited the proper thickness
of copper.

Direction of Current.—If a copper and an
iron plate are put into a copper solution and connected
up in circuit with each other, a primary
battery is thereby formed, which will generate
electricity. In this case, the iron will be positive
and the copper negative, so that the current
within such a cell would flow from the iron (in
this instance, the anode) to the negative, or
cathode.

The action of electroplating reverses this process
and causes the current to flow from the copper
to the iron (in this instance, the cathode).

p. 135

CHAPTER XIVToC

ELECTRIC HEATING, THERMO ELECTRICITY

Generating Heat in a Wire.—When a current
of electricity passes through a conductor, like a
wire, more or less heat is developed in the conductor.
This heat may be so small that it cannot
be measured, but it is, nevertheless, present
in a greater or less degree. Conductors offer a
resistance to the passage of a current, just the
same as water finds a resistance in pipes through
which it passes. This resistance is measured in
ohms, as explained in a preceding chapter, and
it is this resistance which is utilized for electric
heating.

Resistance of Substances.—Silver offers less
resistance to the passage of a current than any
other metal, the next in order is copper, while
iron is, comparatively, a poor conductor.

The following is a partial list of metals, showing
their relative conductivity:

From this table it will be seen that, for instance,
iron offers six and a half times the resistance of
silver, and that German silver has fifteen times
the resistance of silver.

This table is made up of strands of the different
metals of the same diameters and lengths, so as
to obtain their relative values.

Sizes of Conductors.—Another thing, however,
must be understood. If two conductors of the
same metal, having different diameters, receive
the same current of electricity, the small conductor
will offer a greater resistance than the large
conductor, hence will generate more heat. This
can be offset by increasing the diameter of the
conductor. The metal used is, therefore, of importance,
on account of the cost involved.

Comparison of Metals.—A conductor of aluminum,
say, 10 feet long and of the same weight
as copper, has a diameter two and a quarter times
greater than copper; but as the resistance of
aluminum is 50 per cent. more than that of silver,
it will be seen that, weight for weight, copper isp. 137
the cheaper, particularly as aluminum costs fully
three times as much as copper.

Fig. 96. Simple Electric Heater

The table shows that German silver has the
highest resistance. Of course, there are other
metals, like antimony, platinum and the like, which
have still higher resistance. German silver,
however, is most commonly used, although there
are various alloys of metal made which have
high resistance and are cheaper.

The principle of all electric heaters is the same,p. 138
namely, the resistance of a conductor to the passage
of a current, and an illustration of a water
heater will show the elementary principles in all
of these devices.

A Simple Electric Heater.—In Fig. 96 the
illustration shows a cup or holder (A) for the
wire, made of hard rubber. This may be of such
diameter as to fit upon and form the cover for a
glass (B). The rubber should be ½ inch thick.
Two holes are bored through the rubber cup, and
through them are screwed two round-headed
screws (C, D), each screw being 1½ inches long,
so they will project an inch below the cap. Each
screw should have a small hole in its lower end to
receive a pin (E) which will prevent the resistance
wire from slipping off.

The resistance wire (F) is coiled for a suitable
length, dependent upon the current used, one end
being fastened by wrapping it around the screw
(C). The other end of the wire is then brought
upwardly through the interior of the coil and
secured in like manner to the other screw (D).

Caution must be used to prevent the different
coils or turns from touching each other. When
completed, the coil may be immersed in water, the
current turned on, and left so until the water is
sufficiently heated.

Fig. 97. Resistance Device

Fig. 98. Resistance Device

How to Arrange for Quantity of Currentp. 139
Used.—It is difficult to determine just the proper
length the coil should be, or the sizes of the wire,
unless you know what kind of current you have.
You may, however, rig up your own apparatus
for the purpose of making it fit your heater, by
preparing a base of wood (A) 8 inches long, 3
inches wide and 1 inch thick. On this mount
four electric lamp sockets (B). Then connect
the inlet wire (C) by means of short pieces of wire
(D) with all the sockets on one side. The outlet
wire (E) should then be connected up with the
other sides of the sockets by the short wires (F).
If, now, we have one 16-candlepower lamp in one
of the sockets, there is a half ampere going
through the wires (C, F). If there are two lampsp. 140
on the board you will have 1 ampere, and so on.
By this means you may readily determine how
much current you are using and it will also afford
you a means of finding out whether you have too
much or too little wire in your coil to do the
work.

Fig. 99. Plan View of Electric Iron

An Electric Iron.—An electric iron is made in
the same way. The upper side of a flatiron has
a circular or oval depression (A) cast therein,
and a spool of slate (B) is made so it will fit into
the depression and the high resistance wire (C)
is wound around this spool, and insulating material,
such as asbestos, must be used to pack
around it. Centrally, the slate spool has an upwardly
projecting circular extension (D) which
passes through the cap or cover (E) of the iron.
The wires of the resistance coil are then broughtp. 141
through this circular extension and are connected
up with the source of electrical supply. Wires
are now sold for this purpose, which are adapted
to withstand an intense heat.

Fig. 100. Section of Electric Iron

The foregoing example of the use of the current,
through resistance wires, has a very wide
application, and any boy, with these examples
before him, can readily make these devices.

Thermo Electricity.—It has long been the
dream of scientists to convert heat directly into
electricity. The present practice is to use a boiler
to generate steam, an engine to provide the motion,
and a dynamo to convert that motion into
electricity. The result is that there is loss in
the process of converting the fuel heat into steam;
loss to change the steam into motion, and loss top. 142
make electricity out of the motion of the engine.
By using water-power there is less actual loss;
but water-power is not available everywhere.

Converting Heat Directly Into Electricity.—Heat
may be converted directly into electricity
without using a boiler, an engine or a dynamo,
but it has not been successful from a commercial
standpoint. It is interesting, however, to know
and understand the subject, and for that reason
it is explained herein.

Metals; Electric Positive-Negative.—To understand
the principle, it may be stated that all
metals are electrically positive-negative to each
other. You will remember that it has hereinbefore
been stated that if, for instance, iron and
copper are put into an acid solution, a current will
be created or generated thereby. So with zinc
and copper, the usual primary battery elements.
In all such cases an electrolyte is used.

Thermo-electricity dispenses with the electrolyte,
and nothing is used but the metallic elements
and heat. The word thermo means heat. If,
now, we can select two strips of different
metals, and place them as far apart as possible—that
is, in their positive-negative relations with
each other, and unite the end of one with one
end of other by means of a rivet, and then heat
the riveted ends, a current will be generated inp. 143
the strips. If, for instance, we use an iron in
conjunction with a copper strip, the current will
flow from the copper to the iron, because copper
is positive to iron, and iron negative to copper.
It is from this that the term positive-negative is
taken.

The two metals most available, which are thus
farthest apart in the scale of positive-negative
relation, are bismuth and antimony.

Fig. 101. Thermo-Electric Couple

In Fig. 101 is shown a thermo-electric couple
(A, B) riveted together, with thin outer ends
connected by means of a wire (C) to form a
circuit. A galvanometer (D) or other current-testing
means is placed in this circuit. A lamp
is placed below the joined ends.

Thermo-Electric Couples.—Any number of
these couples may be put together and joined at
each end to a common wire and a fairly large flow
of current obtained thereby.

One thing must be observed: A current willp. 144
be generated only so long as there exists a difference
in temperature between the inner and the
outer ends of the bars (A, B). This may be accomplished
by water, or any other cooling means
which may suggest itself.

p. 145

CHAPTER XVToC

ALTERNATING CURRENTS, CHOKING COILS, TRANSFORMERS, CONVERTERS AND RECTIFIERS

Direct Current.—When a current of electricity
is generated by a cell, it is assumed to move along
the wire in one direction, in a steady, continuous
flow, and is called a direct current. This direct
current is a natural one if generated by a
cell.

Alternating Current.—On the other hand, the
natural current generated by a dynamo is alternating
in its character—that is, it is not a direct,
steady flow in one direction, but, instead, it flows
for an instant in one direction, then in the other
direction, and so on.

A direct-current dynamo such as we have shown
in Chapter IV, is much easier to explain, hence it
is illustrated to show the third method used in
generating an electric current.

It is a difficult matter to explain the principle
and operation of alternating current machines,
without becoming, in a measure, too technical for
the purposes of this book, but it is important to
know the fundamentals involved, so that the operation
and uses of certain apparatus, like the chokingp. 146
coil, transformers, rectifiers and converters,
may be explained.

The Magnetic Field.—It has been stated that
when a wire passes through the magnetic field of a
magnet, so as to cut the lines of force flowing out
from the end of a magnet, the wire will receive
a charge of electricity.

Fig. 102. Cutting a Magnetic Field

To explain this, study Fig. 102, in which is a
bar magnet (A). If we take a metal wire (B)
and bend it in the form of a loop, as shown, and
mount the ends on journal-bearing blocks, the wire
may be rotated so that the loop will pass through
the magnetic field. When this takes place, the
wire receives a charge of electricity, which moves,
say, in the direction of the darts, and will make a
complete circuit if the ends of the looped wire
are joined, as shown by the conductor (D).

Action of the Magnetized Wire.—You will remember,
also that we have pointed out how, when
a current passes over a wire, it has a magnetic
field extending out around it at all points, so that
while it is passing through the magnetic field ofp. 147
the magnet (A), it becomes, in a measure, a magnet
of its own and tries to set up in business for
itself as a generator of electricity. But when the
loop leaves the magnetic field, the magnetic or
electrical impulse in the wire also leaves it.

The Movement of a Current in a Charged Wire.—Your
attention is directed, also, to another
statement, heretofore made, namely, that
when a current from a charged wire passes by
induction to a wire across space, so as to charge
it with an electric current, it moves along the
charged wire in a direction opposite to that of
the current in the charging wire.

Now, the darts show the direction in which the
current moves while it is approaching and passing
through the magnetic field. But the moment
the loop is about to pass out of the magnetic field,
the current in the loop surges back in the opposite
direction, and when the loop has made a revolution
and is again entering the magnetic field, it
must again change the direction of flow in the
current, and thus produce alternations in the flow
thereof.

Let us illustrate this by showing the four positions
of the revolving loop. In Fig. 103 the loop
(B) is in the middle of the magnetic field, moving
upwardly in the direction of the curved dart
(A), and while in that position the voltage, or thep. 148
electrical impulse, is the most intense. The current
used flows in the direction of the darts (C)
or to the left.

In Fig. 104, the loop (A) has gone beyond the
influence of the magnetic field, and now the current
in the loop tries to return, or reverse itself,
as shown by the dart (D). It is a reaction that
causes the current to die out, so that when the
loop has reached the point farthest from the magnet,
as shown in Fig. 105, there is no current in
the loop, or, if there is any, it moves faintly in the
direction of the dart (E).

Fig. 103-106. Illustrating Alternations

Current Reversing Itself.—When the loop
reaches its lowest point (Fig. 106) it again comes
within the magnetic field and the current commences
to flow back to its original direction, as
shown by darts (C)

p. 149

Self-Induction.—This tendency of a current
to reverse itself, under the conditions cited, is
called self-induction, or inductance, and it would
be well to keep this in mind in pursuing the
study of alternating currents.

You will see from the foregoing, that the alternations,
or the change of direction of the current,
depends upon the speed of rotation of the loop
past the end of the magnet.

Fig. 107. Form for Increasing Alternations

Fig. 108. Form for Increasing Alternations

Instead, therefore, of using a single loop, we
may make four loops (Fig. 107), which at the
same speed as we had in the case of the single
loop, will give four alternations, instead of one,
and still further, to increase the periods of alternation,
we may use the four loops and two magnets,p. 150
as in Fig. 108. By having a sufficient number
of loops and of magnets, there may be 40,
50, 60, 80, 100 or 120 such alternating periods in
each second. Time, therefore, is an element in
the operation of alternating currents.

Let us now illustrate the manner of connecting
up and building the dynamo, so as to derive the
current from it. In Fig. 109, the loop (A) shows,
for convenience, a pair of bearings (B). A contact
finger (C) rests on each, and to these the
circuit wire (D) is attached. Do not confuse
these contact fingers with the commutator brushes,
shown in the direct-current motor, as they are
there merely for the purpose of making contact
between the revolving loop (A) and stationary
wire (D).

Fig. 109. Connection of Alternating Dynamo Armature

Brushes in a Direct-Current Dynamo.—The
object of the brushes in the direct-current dynamo,
in connection with a commutator, is to convert
this inductance of the wire, or this effort to reverse
itself into a current which will go in onep. 151
direction all the time, and not in both directions
alternately.

To explain this more fully attention is directed
to Figs. 110 and 111. Let A represent the armature,
with a pair of grooves (B) for the wires.
The commutator is made of a split tube, the parts
so divided being insulated from each other, and
in Fig. 110, the upper one, we shall call and designate
the positive (+) and the lower one the negative
(-). The armature wire (C) has one end
attached to the positive commutator terminal and
the other end of this wire is attached to the negative
terminal.

Fig. 110. Direct Current Dynamo

One brush (D) contacts with the positive terminal
of the commutator and the other brushp. 152
(E) with the negative terminal. Let us assume
that the current impulse imparted to the wire
(C) is in the direction of the dart (F, Fig. 110).
The current will then flow through the positive
(+) terminal of the commutator to the brush (D),
and from the brush (D) through the wire (G) to
the brush (E), which contacts with the negative
(-) terminal of the commutator. This will continue
to be the case, while the wire (C) is passing
the magnetic field, and while the brush (D) is
in contact with the positive (+) terminal. But
when the armature makes a half turn, or when it
reaches that point where the brush (D) contacts
with the negative (-) terminal, and the brush
(E) contacts with the positive (+) terminal, ap. 153
change in the direction of the current through the
wire (G) takes place, unless something has happened
to change it before it has reached the
brushes (D, E).

Fig. 111. Circuit Wires in Direct Current Dynamo

Now, this change is just exactly what has happened
in the wire (C), as we have explained.
The current attempts to reverse itself and start
out on business of its own, so to speak, with the
result that when the brushes (D and E) contact
with the negative and positive terminals, respectively,
the surging current in the wire (C) is
going in the direction of the dart (H)—that is,
while, in Fig. 110, the current flows from the wire
(C) into the positive terminal, and out of the negative
terminal into the wire (C), the conditions
are exactly reversed in Fig. 111. Here the current
in wire C flows into the negative (-) terminal,
and from the positive (+) terminal into
the wire C, so that in either case the current will
flow out of the brush D and into the brush E,
through the external circuit (G).

It will be seen, therefore, that in the direct-current
motor, advantage is taken of the surging,
or back-and-forth movement, of the current to
pass it along in one direction, whereas in the
alternating current no such change in direction
is attempted.

Alternating Positive and Negative Poles.p. 154—The
alternating current, owing to this surging
movement, makes the poles alternately positive
and negative. To express this more clearly, supposing
we take a line (A, Fig. 112), which is
called the zero line, or line of no electricity. The
current may be represented by the zigzag line
(B). The lines (B) above zero (A) may be designated
as positive, and those below the line as
negative. The polarity reverses at the line A,
goes up to D, which is the maximum intensity or
voltage above zero, and, when the current falls
and crosses the line A, it goes in the opposite
direction to E, which is its maximum voltage in
the other direction. In point of time, if it takes
one second for the current to go from C to F,
on the down line, then it takes only a half second
to go from C to G, so that the line A represents
the time, and the line H the intensity, a complete
cycle being formed from C, D, F, then through
F, E, C, and so on.

Fig. 112. Alternating Polarity Lines

p. 155

How an Alternating Dynamo Is Made.—It is
now necessary to apply these principles in the construction
of an alternating-current machine. Fig.
113 is a diagram representing the various elements,
and the circuiting.

Fig. 113. Alternating Current Dynamo

Let A represent the ring or frame containing
the inwardly projecting field magnet cores (B). C
is the shaft on which the armature revolves, and
this carries the wheel (D), which has as many
radially disposed magnet cores (E) as there are
of the field magnet cores (B).

The shaft (C) also carries two pulleys with
rings thereon. One of these rings (F) is for onep. 156
end of the armature winding, and the other ring
(G) for the other end of the armature wire.

The Windings.—The winding is as follows:
One wire, as at H, is first coiled around one magnet
core, the turnings being to the right. The
outlet terminal of this wire is then carried to the
next magnet core and wound around that, in the
opposite direction, and so on, so that the terminal
of the wire is brought out, as at I, all of these
wires being connected to binding posts (J, J’),
to which, also, the working circuits are attached.

The Armature Wires.—The armature wires, in
like manner, run from the ring (G) to one armature
core, being wound from right to left, then
to the next core, which is wound to the right, afterward
to the next core, which is wound to the left,
and so on, the final end of the wire being connected
up with the other ring (F). The north
(N) and the south (S) poles are indicated in the
diagram.

Choking Coil.—The self-induction in a current
of this kind is utilized in transmitting electricity
to great distances. Wires offer resistance, or
they impede the flow of a current, as hereinbefore
stated, so that it is not economical to transmit a
direct current over long distances. This can be
done more efficiently by means of the alternating
current, which is subject to far less loss than isp. 157
the case with the direct current. It affords a
means whereby the flow of a current may be
checked or reduced without depending upon the
resistance offered by the wire over which it is
transmitted. This is done by means of what is
called a choking coil. It is merely a coil of wire,
wound upon an iron core, and the current to be
choked passes through the coil. To illustrate this,
let us take an arc lamp designed to use a 50-volt
current. If a current is supplied to it carrying
100 volts, it is obvious that there are 50 volts more
than are needed. We must take care of this excess
of 50 volts without losing it, as would happen
were we to locate a resistance of some kind in the
circuit. This result we accomplish by the introduction
of the choking coil, which has the effect
of absorbing the excessive 50 volts, the action being
due to its quality of self-induction, referred to
in the foregoing.

Fig. 114. Choking Coil

In Fig. 114, A is the choking coil and B an arcp. 158
lamp, connected up, in series, with the choking
coil.

The Transformer.—It is more economical to
transmit 10,000 volts a long distance than 1,000
volts, because the lower the pressure, or the
voltage, the larger must be the conductor to avoid
loss. It is for this reason that 500 volts, or more,
are used on electric railways. For electric light
purposes, where the current goes into dwellings,
even this is too high, so a transformer is used
to take a high-voltage current from the main line
and transform it into a low voltage. This is done
by means of two distinct coils of wire, wound
upon an iron core.

Fig. 115. A Transformer

In Fig. 115 the core is O-shaped, so that a primary
winding (A), from the electrical source, can
be wound upon one limb, and the secondary windingp. 159
(B) wound around the other limb. The wires,
to supply the lamps, run from the secondary coil.
There is no electrical connection between the two
coils, but the action from the primary to the secondary
coil is solely by induction. When a current
passes through the primary coil, the surging
movement, heretofore explained, is transmitted
to the iron core, and the iron core, in
turn, transmits this electrical energy to the secondary
coil.

How the Voltage Is Determined.—The voltage
produced by the secondary coil will depend
upon several things, namely, the strength of the
magnetism transmitted to it; the rapidity, or periodicity
of the current, and the number of turns of
wire around the coil. The voltage is dependent
upon the length of the winding. But the voltage
may also be increased, as well as decreased. If
the primary has, we will say, 100 turns of wire,
and has 200 volts, and the secondary has 50 turns
of wire, the secondary will give forth only one-half
as much as the primary, or 100 volts.

If, on the other hand, 400 volts would be required,
the secondary should have 200 turns in
the winding.

Voltage and Amperage in Transformers.—It
must not be understood that, by increasing the
voltage in this way, we are getting that muchp. 160
more electricity. If the primary coil, with 100
turns, produces a current of 200 volts and 50 amperes,
which would be 200 × 50 = 10,000 watts,
and the secondary coil has 50 turns, we shall have
100 volts and 100 amperes: 100 (V.) × 100 (A.)
= 10,000 watts. Or, if, on the other hand, our
secondary winding is composed of 200 turns, we
shall have 400 volts and 25 amperes, 400 (volts)
× 25 (amperes) also gives 10,000 watts.

Necessarily, there will be some loss, but the
foregoing is offered as the theoretical basis of
calculation.

p. 161

CHAPTER XVIToC

ELECTRIC LIGHTING

The most important step in the electric field,
after the dynamo had been brought to a fairly
workable condition, was its utilization to make
light. It was long known prior to the discovery
of practical electric dynamos, that the electric
current would produce an intense heat.

Ordinary fuels under certain favorable conditions
will produce a temperature of 4,500 degrees
of heat; but by means of the electric arc, as high
as six, eight and ten thousand degrees are available.

The fact that when a conductor, in an electric
current, is severed, a spark will follow the drawing
part of the broken ends, led many scientists to
believe, even before the dynamo was in a practical
shape, that electricity, sooner or later, would
be employed as the great lighting agent.

When the dynamo finally reached a stage in development
where its operation could be depended
on, and was made reversible, the first active steps
were taken to not only produce, but to maintain
an arc between two electrodes.

It would be difficult and tedious to follow out thep. 162
first experiments in detail, and it might, also, be
useless, as information, in view of the present
knowledge of the science. A few steps in the
course of the development are, however, necessary
to a complete understanding of the subject.

Reference has been made in a previous chapter
to what is called the Electric Arc, produced by
slightly separated conductors, across which the
electric current jumps, producing the brilliantly
lighted area.

This light is produced by the combustion of the
carbon of which the electrodes are composed.
Thus, the illumination is the result of directly
burning a fuel. The current, in passing from one
electrode to the other, through the gap, produces
such an intense heat that the fuel through which
the current passes is consumed.

Carbon in a comparatively pure state is difficult
to ignite, owing to its great resistance to heat.
At about 7,000 degrees it will fuse, and pass into
a vapor which causes the intense illumination.

The earliest form of electric lighting was by
means of the arc, in which the light is maintained
so long as the electrodes were kept a certain distance
apart.

To do this requires delicate mechanism, for the
reason that when contact is made, and the current
flows through the two electrodes, which are connectedp. 163
up directly with the coils of a magnet, the
cores, or armatures, will be magnetized. The result
is that the electrode, connected with the
armature of the magnet, is drawn away from the
other electrode, and the arc is formed, between
the separated ends.

As the current also passes through a resistance
coil, the moment the ends of the electrodes are
separated too great a distance, the resistance prevents
a flow of the normal amount of current,
and the armature is compelled to reduce its pull.
The effect is to cause the two electrodes to again
approach each other, and in doing so the arc becomes
brighter.

It will be seen, therefore, that there is a constant
fight between the resistance coil and the
magnet, the combined action of the two being such,
that, if properly arranged, and with powers in
correct relation to each other, the light may be
maintained without undue flickering. Such devices
are now universally used, and they afford
a steady and reliable means of illumination.

Many improvements are made in this direction,
as well as in the ingredients of the electrodes. A
very novel device for assuring a perfect separation
at all times between the electrodes, is by
means of a pair of parallel carbons, held apart by
a non-conductor such as clay, or some mixture ofp. 164
earth, a form of which is shown in Fig. 116.

The drawing shows two electrodes, separated
by a non-conducting material, which is of such
a character that it will break down and
crumble away, as the ends of the electrodes burn
away.

Fig. 116. Parallel Carbons.

This device is admirable where the alternating
current is used, because the current moves back
and forth, and the two electrodes are thus burned
away at the same rate of speed.

In the direct or continuous current the movementp. 165
is in one direction only, and as a result the
positive electrode is eaten away twice as fast as
the negative.

This is the arc form of lamp universally used
for lighting large spaces or areas, such as streets,
railway stations, and the like. It is important also
as the means for utilizing searchlight illumination,
and frequently for locomotive headlights.

Arc lights are produced by what is called the
series current. This means that the lamps are all
connected in a single line. This is illustrated by
reference to Fig. 117, in which A represents the
wire from the dynamo, and B, C the two electrodes,
showing the current passing through from
one lamp to the next.

Fig. 117. Arc-Lighting Circuit.

A high voltage is necessary in order to cause the
current to leap across the gap made by the separation
of the electrodes

p. 166

The Incandescent System.—This method is entirely
different from the arc system. It has been
stated that certain metals conduct electricity
with greater facility than others, and some have
higher resistance than others. If a certain amount
of electricity is forced through some metals, they
will become heated. This is true, also, if metals,
which, ordinarily, will conduct a current freely, are
made up into such small conductors that it is
difficult for the current to pass.

Fig. 118. Interrupted Conductor.

In the arc method high voltage is essential; in
the incandescent plan, current is the important
consideration. In the arc, the light is produced
by virtue of the break in the line of the conductor;
in the incandescent, the system is closed at all
times.

Supposing we have a wire A, a quarter of an
inch in diameter, carrying a current of, say, 500
amperes, and at any point in the circuit the wire
is made very small, as shown at B, in Fig. 118, it
is obvious that the small wire would not be large
enough to carry the current.

The result would be that the small connectionp. 167
B would heat up, and, finally, be fused. While the
large part of the wire would carry 500 amperes,
the small wire could not possibly carry more than,
say, 10 amperes. Now these little wires are the
filaments in an electric bulb, and originally the attempt
was made to have them so connected up
that they could be illuminated by a single wire,
as with the arc system above explained, one following
the other as shown in Fig. 117.

Fig. 119. Incandescent Circuit.

It was discovered, however, that the addition of
each successive lamp, so wired, would not give
light in proportion to the addition, but at only
about one-fourth the illumination, and such a
course would, therefore, make electric lighting
enormously expensive.

This knowledge resulted in an entirely new system
of wiring up the lamps in a circuit. This is
explained in Fig. 119. In this figure A represents
the dynamo, B, B the brushes, C, D the two linep. 168
wires, E the lamps, and F the short-circuiting
wires between the two main conductors
C, D.

It will be observed that the wires C, D are
larger than the cross wires F. The object is to
show that the main wires might carry a very heavy
amperage, while the small cross wires F require
only a few amperes.

This is called the multiple circuit, and it is obvious
that the entire amperage produced by the
dynamo will not be required to pass through each
lamp, but, on the other hand, each lamp takes only
enough necessary to render the filament incandescent.

This invention at once solved the problem of the
incandescent system and was called the subdivision
of the electric light. By this means the cost
was materially reduced, and the wiring up and
installation of lights materially simplified.

But the divisibility of the light did not, by any
means, solve the great problem that has occupied
the attention of electricians and experimenters
ever since. The great question was and is to preserve
the little filament which is heated to incandescence,
and from which we get the light.

The effort of the current to pass through the
small filament meets with such a great resistance
that the substance is heated up. If it is made ofp. 169
metal there is a point at which it will fuse, and
thus the lamp is destroyed.

It was found that carbon, properly treated,
would heat to a brilliant white heat without fusing,
or melting, so that this material was employed.
But now followed another difficulty. As this intense
heat consumed the particles of carbon, owing
to the presence of oxygen, means were sought to
exclude the air.

This was finally accomplished by making a bulb
of glass, from which the air was exhausted, and as
such a globe had no air to support combustion,
the filaments were finally made so that they would
last a long time before being finally disintegrated.

The quest now is, and has been, to find some material
of a purely metallic character, which will
have a very high fusing point, and which will,
therefore, dispense with the cost of the exhausted
bulb. Some metals, as for instance, osmium, tantalum,
thorium, and others, have been used, and
others, also, with great success, so that the march
of improvements is now going forward with rapid
strides.

Vapor Lamps.—One of the directions in which
considerable energy has been directed in the past,
was to produce light from vapors. The Cooper
Hewitt mercury vapor lamp is a tube filled with
the vapor of mercury, and a current is sent throughp. 170
the vapor which produces a greenish light, and
owing to that peculiar color, has not met with much
success.

It is merely cited to show that there are other directions
than the use of metallic conductors and
filaments which will produce light, and the day
is no doubt close at hand when we may expect
some important developments in the production
of light by means of the Hertzian waves.

Directions for Improvements.—Electricity,
however, is not a cheap method of illumination.
The enormous heat developed is largely wasted.
The quest of the inventor is to find a means whereby
light can be produced without the generation
of the immense heat necessary.

Man has not yet found a means whereby he can
make a heat without increasing the temperature,
as nature does it in the glow worm, or in the firefly.
A certain electric energy will produce both
light and heat, but it is found that much more of
this energy is used in the heat than in the
light.

What wonderful possibilities are in store for the
inventor who can make a heatless light! It is a
direction for the exercise of ingenuity that will
well repay any efforts

p. 171

Curious Superstitions Concerning Electricity

Electricity, as exhibited in light, has been the
great marvel of all times. The word electricity
itself comes from the thunderbolt of the ancient
God Zeus, which is known to be synonymous with
the thunderbolt and the lightning.

Magnetism, which we know to be only another
form of electricity, was not regarded the same as
electricity by the ancients. Iron which had the
property to attract, was first found near the town
of Magnesia, in Lydia, and for that reason was
called magnetism.

Later on, a glimmer of the truth seemed to dawn
on the early scientists, when they saw the resemblance
between the actions of the amber and the
loadstone, as both attracted particles. And here
another curious thing resulted. Amber will attract
particles other than metals. The magnet
did not; and from this imperfect observation and
understanding, grew a belief that electricity, or
magnetism would attract all substances, even human
flesh, and many devices were made from magnets,
and used as cures for the gout, and to affect
the brain, or to remove pain.

Even as early as 2,500 years before the birth
of Christ the Chinese knew of the properties of
the magnet, and also discovered that a bar of thep. 172
permanent magnet would arrange itself north and
south, like the mariners’ compass. There is no
evidence, however, that it was used as a mariner’s
compass until centuries afterwards.

But the matter connected with light, as an electrical
development, which interests us, is its manifestations
to the ancients in the form of lightning.
The electricity of the earth concentrates itself on
the tops of mountains, or in sharp peaks, and accounts
for the magnificent electrical displays
always found in mountainous regions.

Some years ago, a noted scientist, Dr. Siemens,
while standing on the top of the great pyramid of
Cheops, in Egypt, during a storm, noted that an
electrical discharge flowed from his hand when extended
toward the heavens. The current manifested
itself in such a manner that the hissing
noise was plainly perceptible.

The literature of all ages and of all countries
shows that this manifestation of electrical discharges
was noted, and became the subject of discussions
among learned men.

All these displays were regarded as the bolts
of an angry God, and historians give many accounts
of instances where, in His anger, He sent
down the lightning to destroy.

Among the Romans Jupiter thus hurled forth
his wrath; and among many ancient people, evenp. 173
down to the time of Charlemagne, any space
struck by lightning was considered sacred, and
made consecrated ground.

From this grew the belief that it was sacrilegious
to attempt to imitate the lightning of the sky—that
Deity would visit dire punishment on any
man who attempted to produce an electric light.
Virgil relates accounts where certain princes attempted
to imitate the lightning, and were struck
by thunderbolts as punishments.

Less than a century ago Benjamin Franklin devised
the lightning rod, in order to prevent lightning
from striking objects. The literature of that
day abounds with instances of protests made, on
the part of those who were as superstitions as the
people in ancient times, who urged that it was
impious to attempt to ward off Heaven’s lightnings.
It was argued that the lightning was one
way in which the Creator manifested His displeasure,
and exercised His power to strike the wicked.

When such writers as Pliny will gravely set
forth an explanation of the causes of lightning, as
follows in the paragraph below, we can understand
why it inculcated superstitious fears in the people
of ancient times. He says:

“Most men are ignorant of that secret, which,
by close observation of the heavens, deep scholars
and principal men of learning have found out,p. 174
namely, that they are the fires of the uppermost
planets, which, falling to the earth, are called lightning;
but those especially which are seated in the
middle, that is about Jupiter, perhaps because participating
in the excessive cold and moisture from
the upper circle of Saturn, and the immoderate
heat of Mars, that is next beneath, by this means
he discharges his superfluity, and therefore it is
commonly said, ‘That Jupiter shooteth and darteth
lightning.’ Therefore, like as out of a burning
piece of wood a coal flieth forth with a crack, even
so from a star is spit out, as it were, and voided
forth this celestial fire, carrying with it presages
of future things; so that the heavens showeth divine
operations, even in these parcels and portions
which are rejected and cast away as superfluous.”

p. 175

CHAPTER XVIIToC

POWER, AND VARIOUS OTHER ELECTRICAL MANIFESTATIONS

It would be difficult to mention any direction in
human activity where electricity does not serve as
an agent in some form or manner. Man has
learned that the Creator gave this great power
into the hands of man to use, and not to curse.

When the dynamo was first developed it did not
appear possible that it could generate electricity,
and then use that electricity in order to turn the
dynamo in the opposite direction. It all seems so
very natural to us now, that such a thing should
practically follow; but man had to learn this.

Let us try to make the statement plain by a few
simple illustrations. By carefully going over the
chapter on the making of the dynamo, it will be
evident that the basis of the generation of the current
depends on the changing of the direction of
the flow of an electric current.

Look at the simple horse-shoe magnet. If two
of them are gradually moved toward each other,
so that the north pole of one approaches the north
pole of the other, there is a sensible attempt for
them to push away from each other. If, however,p. 176
one of them is turned, so that the north pole of
one is opposite the south pole of the other, they
will draw together.

In this we have the foundation physical action
of the dynamo and the motor. When power is applied
to an armature, and it moves through a magnetic
field, the action is just the same as in the case
of the hand drawing the north and the south pole
of the two approaching magnets from each other.

The influence of the electrical disturbance produced
by that act permeated the entire winding of
the field and armature, and extended out on the
whole line with which the dynamo was connected.
In this way a current was established and transmitted,
and with proper wires was sent in the form
of circuits and distributed so as to do work.

But an electric current, without suitable mechanism,
is of no value. It must have mechanism to
use it, as well as to make it. In the case of
light, we have explained how the arc and the incandescent
lamps utilize it for that purpose.

But now, attempting to get something from it
in the way of power, means another piece of mechanism.
This is done by the motor, and this motor
is simply a converter, or a device for reversing
the action of the electricity.

Attention is called to Figs. 120 and 121. Let us
assume that the field magnets A, A are the positives,p. 177
and the magnets B, B the negatives. The revolving
armature has also four magnet coils, two
of them, C, C, being positive, and the other two,
D, D, negative, each of these magnet coils being so
connected up that they will reverse the polarities
of the magnets.

Figs. 120-121. Action of Magnets in a Dynamo

Now in the particular position of the revolving
armature, in Fig. 120, the magnets of the armature
have just passed the respective poles of the field
magnets, and the belt E is compelled to turn the
armature past the pole pieces by force in the direction
of the arrow F. After the armature magnets
have gone to the positions in Fig. 121, the positives
A try to draw back the negatives D of the
armature, and at the same time the negatives B
repel the negatives D, because they are of the same
polarities

p. 178

This repulsion of the negatives A, B continues
until the armature poles C, D have slightly passed
them, when the polarities of the magnets C, D are
changed; so that it will be seen, by reference to
Fig. 122, that D is now retreating from B, and C
is going away from A—that is, being forced away
contrary to their natural attractive influences, and
in Fig. 123, when the complete cycle is nearly finished,
the positives are again approaching each
other and the negatives moving together.

Figs. 122-123. Cycle Action in Dynamo

In this manner, at every point, the sets of magnets
are compelled to move against their magnetic
pull. This explains the dynamo.

Now take up the cycle of the motor, and note in
Fig. 124 that the negative magnets D of the armature
are closely approaching the positive and negativep. 179
magnets, on one side; and the positive magnets
C are nearing the positive and negatives on
the other side. The positives A, therefore, attract
the negatives D, and the negative B exert a pull
on the positives C at the same time. The result is
that the armature is caused to revolve, as shown
by the dart G, in a direction opposite to the dart in
Fig. 120.

Figs. 124-125. Action of Magnets in Motor

When the pole pieces of the magnets C, D are
about to pass magnets A, B, as shown in Fig. 125,
it is necessary to change the polarities of the armature
magnets C, D; so that by reference to Fig.
126, it will be seen that they are now indicated as
C-, and D+, respectively, and have moved to a
point midway between the poles A, B (as in Fig.
125), where the pull on one side, and the push onp. 180
the other are again the same, and the last Figure
127 shows the cycle nearly completed.

The shaft of the motor armature is now the element
which turns the mechanism which is to be operated.
To convert electrical impulses into power,
as thus shown, results in great loss. The first step
is to take the steam boiler, which is the first stage
in that source which is the most common and universal,
and by means of fuel, converting water into
steam. The second is to use the pressure of this
steam to drive an engine; the third is to drive the
dynamo which generates the electrical impulse;
and the fourth is the conversion from the dynamo
into a motor shaft. Loss is met with at each step,
and the great problem is to eliminate this waste.

Figs. 126-127. Positions of Magnets in Motor

The great advantage of electrical power is not inp. 181
utilizing it for consumption at close ranges, but
where it is desired to transmit it for long distances.
Such illustrations may be found in electric
railways, and where water power can be obtained
as the primal source of energy, the cost is not excessive.
It is found, however, that even with the
most improved forms of mechanism, in electrical
construction, the internal combustion engines are
far more economical.

Transmission of Energy

One of the great problems has been the transmission
of the current to great distances. By using a
high voltage it may be sent hundreds of miles, but
to use a current of that character in the cars, or
shops, or homes, would be exceedingly dangerous.

To meet this requirement transformers have
been devised, which will take a current of very
high voltage, and deliver a current of low tension,
and capable of being used anywhere with the ordinary
motors.

The Transformer.—This is an electrical device
made up of a core or cores of thin sheet metal,
around which is wound sets of insulated wires, one
set being designed to receive the high voltage, and
the other set to put out the low voltage, as described
in a former chapter

p. 182

These may be made where the original output is
a very high voltage, so that they will be stepped
down, first from one voltage to a lower, and then
from that to the next lower stage. This is called
the “Step down” transformer, and is now used
over the entire world, where large voltages are
generated.

Electric Furnaces.—The most important development
of electricity in the direction of heat is
its use in furnaces. As before stated, an intense
heat is capable of being generated by the electric
current, so that it becomes the great agent to use
for the treatment of refractory material.

In furnaces of this kind the electric arc is the
mechanical form used to produce the great heat,
the only difference being in the size of the apparatus.
The electric furnace is simply an immense
form of arc light, capable of taking a high
voltage, and such an arc is enclosed within a suitable
oven of refractory material, which still further
conserves the heat.

Welding By Electricity.—The next step is to
use the high heat thus capable of being produced,
to fuse metals so that they may be welded together.
It is a difficult matter to unite two large pieces of
metal by the forging method, because the highest
heat is required, owing to their bulk, and in additionp. 183
immense hammers, weighing tons, must be
employed.

Electric welding offers a simple and easy
method of accomplishing the result, and in the
doing of which it avoids the oxidizing action of
the forging heat. Instead of heating the pieces to
be welded in a forge, as is now done, the ends to
be united are simply brought into contact, and the
current is sent through the ends until they are in
a soft condition, after which the parts are pressed
together and united by the simple merging of the
plastic condition in which they are reduced by the
high electric heat.

This form of welding makes the most perfect
joint, and requires no hammering, as the mass of
the metal flows from one part or end to the other;
the unity is a perfect one, and the advantage is
that the metals can be kept in a semi-fluid state for
a considerable time, thus assuring a perfect admixture
of the two parts.

With the ordinary form of welding it is necessary
to drive the heated parts together without
any delay, and at the least cooling must be reheated,
or the joint will not be perfect.

The smallest kinds of electric heating apparatus
are now being made, so that small articles, sheet
metal, small rods, and like parts can be united
with the greatest facility.

p. 184

CHAPTER XVIIIToC

X-RAY, RADIUM, AND THE LIKE

The camera sees things invisible to the human
eye. Its most effective work is done with beams
which are beyond human perception. The photographer
uses the Actinic rays. Ordinary light is
composed of the seven primary colors, of which
the lowest in the scale is the red, and the highest
to violet.

Those below the red are called the Infra-red,
and they are the Hertzian waves, or those used in
wireless telegraphy. Those above the violet are
called Ultra-violet, and these are employed for
X-ray work. The former are produced by the high
tension electric apparatus, which we have described
in the chapter relating to wireless telegraphy;
and the latter, called also the Roentgen
rays, are generated by the Crookes’ Tube.

This is a tube from which all the atmosphere has
been extracted so that it is a practical vacuum.
Within this are placed electrodes so as to divert
the action of the electrical discharge in a particular
direction, and this light, when discharged, is
of such a peculiar character that its discovery
made a sensation in the scientific world

p. 185

The reason for this great wonder was not in the
fact that it projected a light, but because of its
character. Ordinary light, as we see it with the
eye, is capable of being reflected, as when we look
into a mirror at an angle. The X-ray will not reflect,
but instead, pass directly through the glass.

Then, ordinary light is capable of refraction.
This is shown by a ray of light bending as it passes
through a glass of water, which is noticed when
the light is at an angle to the surface.

The X-ray will pass through the water without
being changed from a straight line. The foregoing
being the case, it was but a simple step to conclude
that if it were possible to find a means whereby
the human eye could see within the ultra-violet
beam, it would be possible to see through opaque
substances.

From the discovery so important and far reaching
it was not long until it was found that if the
ultra-violet rays, thus propagated, were transmitted
through certain substances, their rates of vibration
would be brought down to the speeds which
send forth the visible rays, and now the eye is
able to see, in a measure at least, what the actinic
rays show.

This discovery was but the forerunner of a still
more important development, namely, the discovery
of radium. The actual finding of the metalp. 186
was preceded by the knowledge that certain minerals,
and water, as well, possessed the property
of radio-activity.

Radio-activity is a word used to express that
quality in metals or other material by means of
which obscure rays are emitted, that have the capacity
of discharging electrified bodies, and the
power to ionize gases, as well as to actually affect
photograph plates.

Certain metals had this property to a remarkable
degree, particularly uranium, thorium, polonium,
actinium, and others, and in 1898 the Curies,
husband and wife, French chemists, isolated an
element, very ductile in its character, which was a
white metal, and had a most brilliant luster.

Pitchblende, the base metal from which this
was extracted, was discovered to be highly radio-active,
and on making tests of the product taken
from it, they were surprised to find that it emitted
a form of energy that far exceeded in calculations
any computations made on the basis of radio-activity
in the metals hitherto examined.

But this was not the most remarkable part of
the developments. The energy, whatever it was,
had the power to change many other substances if
brought into close proximity. It darkens the color
of diamonds, quartz, mica, and glass. It changes
some of the latter in color, some kinds beingp. 187
turned to brown and others into violet or purple
tinges.

Radium has the capacity to redden the skin, and
affect the flesh of persons, even at some considerable
distance, and it is a most powerful germicide,
destroying bacteria, and has been found also to
produce some remarkable cures in diseases of a
cancerous nature.

The remarkable similarity of the rays propagated
by this substance, with the X-rays, lead
many to believe that they are electrical in their
character, and the whole scientific world is now
striving to use this substance, as well as the more
familiar light waves of the Roentgen tube, in the
healing of diseases.

It is not at all remarkable that this use of it
should first be considered, as it has been the history
of the electrical developments, from the
earliest times, that each successive stage should
find advocates who would urge its virtues to heal
the sick.

It was so when the dynamo was invented, when
the high tension current was produced; and electrical
therapeutics became a leading theme when
transmission by induction became recognized as
a scientific fact.

It is not many years since the X-rays were discovered,p. 188
and the first announcement was concerning
its wonderful healing powers.

This was particularly true in the case of radium,
but for some reason, after the first tests, all experimenters
were thwarted in their theories, because
the science, like all others, required infinite
patience and experience. It was discovered, in the
case of the X-ray, that it must be used in a modified
form, and accordingly, various modifications
of the waves were introduced, called the m and the
n rays, as well as many others, each having some
peculiar qualification.

In time, no doubt, the investigators will find the
right quality for each disease, and learn how to
apply it. Thus, electricity, that most alluring
thing which, in itself, cannot be seen, and is of
such a character that it cannot even be defined in
terms which will suit the exact scientific mind, is
daily bringing new wonders for our investigation
and use.

It is, indeed, a study which is so broad that it
has no limitations, and a field which never will be
exhausted.

THE END

p. 189

GLOSSARY OF WORDS
USED IN TEXT OF THIS VOLUMEToC

p. 207

INDEXToC