Transcriber’s Note: Italics are enclosed in _underscores_. Additional
notes will be found near the end of this ebook.
[Illustration: (cover)]
“ROMANCE OF REALITY” SERIES
Edited by ELLISON HAWKS
ELECTRICITY
_VOLUMES ALREADY ISSUED_
1. THE AEROPLANE. By GRAHAME WHITE and HARRY HARPER.
2. THE MAN-OF-WAR. By Commander E. H. CURREY, R.N.
3. MODERN INVENTIONS. By V. E. JOHNSON, M.A.
4. ELECTRICITY. By W. H. MCCORMICK.
5. ENGINEERING. By GORDON D. KNOX.
[Illustration: THE MARCONI TRANSATLANTIC WIRELESS STATION AT GLACE BAY,
NOVA SCOTIA
Drawing by Irene Sutcliffe]
_“ROMANCE OF REALITY” SERIES_
ELECTRICITY
BY
W. H. McCORMICK
[Illustration]
NEW YORK
FREDERICK A. STOKES COMPANY
PUBLISHERS
_Printed in Great Britain_
PREFACE
I gladly take this opportunity of acknowledging the generous assistance
I have received in the preparation of this book.
I am indebted to the following firms for much useful information
regarding their various specialities:--
Chloride Electrical Storage Co. Ltd.; General Electric Co. Ltd.; Union
Electric Co. Ltd.; Automatic Electric Co., Chicago; Westinghouse
Cooper-Hewitt Co. Ltd.; Creed, Bille & Co. Ltd.; India Rubber, Gutta
Percha, and Telegraph Works Co. Ltd.; W. Canning & Co.; C. H. F.
Muller; Ozonair Ltd.; Universal Electric Supply Co., Manchester; and
the Agricultural Electric Discharge Co. Ltd.
For illustrations my thanks are due to:--
Marconi’s Wireless Telegraph Co. Ltd.; Chloride Electrical Storage Co.
Ltd.; Harry W. Cox & Co. Ltd.; C. H. F. Muller; W. Canning & Co.; Union
Electric Co. Ltd.; Creed, Bille & Co. Ltd.; Ozonair Ltd.; Kodak Ltd.;
C. A. Parsons & Co.; Lancashire Dynamo and Motor Co. Ltd.; Dick, Kerr &
Co. Ltd.; Siemens Brothers Dynamo Works Ltd.; Vickers Ltd.; and Craven
Brothers Ltd.
Mr. Edward Maude and Mr. J. A. Robson have most kindly prepared for me
a number of the diagrams, and I am indebted to Dr. Myer Coplans for
particulars and a diagram of the heat-compensated salinometer.
I acknowledge also many important suggestions from Miss E. C. Dudgeon
on Electro-Culture, and from Mr. R. Baxter and Mr. G. Clark on
Telegraphy and Telephony.
Amongst the many books I have consulted I am indebted specially to
_Electricity in Modern Medicine_, by Alfred C. Norman, M.D.; _Growing
Crops and Plants by Electricity_, by Miss E. C. Dudgeon; and _Wireless
Telegraphy_ (Cambridge Manuals), by Prof. C. L. Fortescue. I have
derived great assistance also from the _Wireless World_.
Finally, I have to thank Mr. Albert Innes, A.I.E.E., of Leeds, for a
number of most valuable suggestions, and for his kindness in reading
through the proofs.
W. H. McC.
LEEDS, 1915
CONTENTS
CHAPTER PAGE
I. THE BIRTH OF THE SCIENCE OF ELECTRICITY 1
II. ELECTRICAL MACHINES AND THE LEYDEN JAR 9
III. ELECTRICITY IN THE ATMOSPHERE 18
IV. THE ELECTRIC CURRENT 27
V. THE ACCUMULATOR 38
VI. MAGNETS AND MAGNETISM 44
VII. THE PRODUCTION OF MAGNETISM BY ELECTRICITY 56
VIII. THE INDUCTION COIL 61
IX. THE DYNAMO AND THE ELECTRIC MOTOR 66
X. ELECTRIC POWER STATIONS 75
XI. ELECTRICITY IN LOCOMOTION 83
XII. ELECTRIC LIGHTING 93
XIII. ELECTRIC HEATING 109
XIV. ELECTRIC BELLS AND ALARMS 116
XV. ELECTRIC CLOCKS 124
XVI. THE TELEGRAPH 128
XVII. SUBMARINE TELEGRAPHY 144
XVIII. THE TELEPHONE 154
XIX. SOME TELEGRAPHIC AND TELEPHONIC INVENTIONS 171
XX. WIRELESS TELEGRAPHY AND TELEPHONY--PRINCIPLES AND
APPARATUS 179
XXI. WIRELESS TELEGRAPHY--PRACTICAL APPLICATIONS 203
XXII. ELECTROPLATING AND ELECTROTYPING 213
XXIII. INDUSTRIAL ELECTROLYSIS 224
XXIV. THE RÖNTGEN RAYS 228
XXV. ELECTRICITY IN MEDICINE 241
XXVI. OZONE 247
XXVII. ELECTRIC IGNITION 253
XXVIII. ELECTRO-CULTURE 258
XXIX. SOME RECENT APPLICATIONS OF ELECTRICITY--AN ELECTRIC
PIPE LOCATOR, ETC. 266
XXX. ELECTRICITY IN WAR 274
XXXI. WHAT IS ELECTRICITY? 287
INDEX 295
LIST OF PLATES
PLATE IN COLOUR: THE MARCONI TRANSATLANTIC WIRELESS STATION AT
GLACE BAY, NOVA SCOTIA _Frontispiece_
FACING PAGE
HYDRO-ELECTRIC POWER STATION 30
(_a_) EXPERIMENT TO SHOW MAGNETIC INDUCTION 48
(_b_) EXPERIMENT TO SHOW THE PRODUCTION OF MAGNETISM BY AN
ELECTRIC CURRENT 48
(_a_) LINES OF MAGNETIC FORCE OF TWO OPPOSITE POLES 50
(_b_) LINES OF MAGNETIC FORCE OF TWO SIMILAR POLES 50
A TYPICAL DYNAMO AND ITS PARTS 70
LOTS ROAD ELECTRIC POWER STATION, CHELSEA 76
POWER STATION BATTERY OF ACCUMULATORS 80
ELECTRIC COLLIERY RAILWAY 86
TYPICAL ELECTRIC LOCOMOTIVES 90
NIGHT PHOTOGRAPHS, TAKEN BY THE LIGHT OF THE ARC LAMPS 96
WHERE ELECTRICAL MACHINERY IS MADE 120
SPECIMEN OF THE WORK OF THE CREED HIGH-SPEED PRINTING TELEGRAPH 140
LARGE ELECTRIC TRAVELLING CRANE AT A RAILWAY WORKS 164
(_a_) MARCONI OPERATOR RECEIVING A MESSAGE 188
(_b_) MARCONI MAGNETIC DETECTOR 188
RÖNTGEN RAY PHOTOGRAPH OF BRITISH AND FOREIGN FOUNTAIN PENS 240
BACHELET “FLYING TRAIN” AND ITS INVENTOR 272
(_a_) CAVALRY PORTABLE WIRELESS CART SET 280
(_b_) AEROPLANE FITTED WITH WIRELESS TELEGRAPHY 280
ELECTRICITY
CHAPTER I
THE BIRTH OF THE SCIENCE OF ELECTRICITY
Although the science of electricity is of comparatively recent date,
electricity itself has existed from the beginning of the world. There
can be no doubt that man’s introduction to electricity was brought
about through the medium of the thunderstorm, and from very early
times come down to us records of the terror inspired by thunder and
lightning, and of the ways in which the ancients tried to account for
the phenomena. Even to-day, although we know what lightning is and how
it is produced, a severe thunderstorm fills us with a certain amount of
awe, if not fear; and we can understand what a terrifying experience it
must have been to the ancients, who had none of our knowledge.
These early people had simple minds, and from our point of view they
had little intelligence; but they possessed a great deal of curiosity.
They were just as anxious to explain things as we are, and so they
were not content until they had invented an explanation of lightning
and thunder. Their favourite way of accounting for anything they
did not understand was to make up a sort of romance about it. They
believed that the heavens were inhabited by various gods, who showed
their pleasure or anger by signs, and so they naturally concluded
that thunder was the voice of angry gods, and lightning the weapon
with which they struck down those who had displeased them. Prayers and
sacrifices were therefore offered to the gods, in the hope of appeasing
their wrath.
Greek and Roman mythology contains many references to thunder and
lightning. For instance, we read about the great god Zeus, who wielded
thunder-bolts which had been forged in underground furnaces by the
giant Cyclops. There was no doubt that the thunder-bolts were made
in this way, because one only had to visit a volcano in order to see
the smoke from the furnace, and hear the rumbling echo of the far-off
hammering. Then we are told the tragic story of Phaeton, son of the
Sun-god. This youth, like many others since his time, was daring and
venturesome, and imagined that he could do things quite as well as
his father. On one occasion he tried to drive his father’s chariot,
and, as might have been expected, it got beyond his control, and came
dangerously near the Earth. The land was scorched, the oceans were
dried up, and the whole Earth was threatened with utter destruction.
In order to prevent such a frightful catastrophe, Jupiter, the mighty
lord of the heavens, hurled a thunder-bolt at Phaeton, and struck him
from the chariot into the river Po. A whole book could be written about
these ancient legends concerning the thunderstorm, but, interesting as
they are, they have no scientific value, and many centuries were to
elapse before the real nature of lightning was understood.
In order to trace the first glimmerings of electrical knowledge we
must leave the thunderstorm and pass on to more trivial matters. On
certain sea-coasts the ancients found a transparent yellow substance
capable of taking a high polish, and much to be desired as an ornament;
and about 600 years B.C. it was discovered that this substance, when
rubbed, gained the power of drawing to it bits of straw, feathers,
and other light bodies. This discovery is generally credited to a
Greek philosopher named Thales, 941–563 B.C., and it must be regarded
as the first step towards the foundation of electrical science.
The yellow substance was amber. We now know it to be simply a sort
of fossilized resin, but the Greeks gave it a much more romantic
origin. When Phaeton’s rashness brought him to an untimely end, his
sorrowing sisters, the Heliades, were changed into poplar trees, and
their tears into amber. Amongst the names given to the Sun-god was
Alector, which means the shining one, and so the tears of the Heliades
came to have the name Electron, or the shining thing. Unlike most
of the old legends, this story of the fate of the Sun-maidens is of
great importance to us, for from the word “electron” we get the name
Electricity.
Thales and his contemporaries seem to have made no serious attempts
to explain the attraction of the rubbed amber, and indeed so little
importance was attached to the discovery that it was completely
forgotten. About 321 B.C. one Theophrastus found that a certain mineral
called “lyncurium” gained attractive powers when rubbed, but again
little attention was paid to the matter, and astonishing as it may
seem, no further progress worth mention was made until towards the
close of the sixteenth century, when Doctor Gilbert of Colchester
began to experiment seriously. This man was born about 1543, and took
his degree of doctor of medicine at Cambridge in 1569. He was very
successful in his medical work, and became President of the College
of Physicians, and later on physician to Queen Elizabeth. He had a
true instinct for scientific research, and was not content to accept
statements on the authority of others, but tested everything for
himself. He found that sulphur, resin, sealing-wax, and many other
substances behaved like amber when rubbed, but he failed to get any
results from certain other substances, such as the metals. He therefore
called the former substances “electrics,” and the latter “anelectrics,”
or non-electrics. His researches were continued by other investigators,
and from him dates the science of electricity.
[Illustration: FIG. 1.--Suspended pith ball for showing electric
attraction.]
Leaving historical matters for the present, we will examine the curious
power which is gained by substances as the result of rubbing. Amber
is not always obtainable, and so we will use in its place a glass rod
and a stick of sealing-wax. If the glass rod is rubbed briskly with a
dry silk handkerchief, and then held close to a number of very small
bits of paper, the bits are immediately drawn to the rod, and the same
thing occurs if the stick of sealing-wax is substituted for the glass.
This power of attraction is due to the presence of a small charge of
electricity on the rubbed glass and sealing-wax, or in other words,
the two substances are said to be electrified. Bits of paper are
unsatisfactory for careful experimenting, and instead of them we will
use the simple piece of apparatus shown in Fig. 1. This consists of a
ball of elder pith, suspended from a glass support by means of a silk
thread. If now we repeat our experiments with the electrified glass or
sealing-wax we find that the little ball is attracted in the same way
as the bits of paper. But if we look carefully we shall notice that
attraction is not the only effect, for as soon as the ball touches the
electrified body it is driven away or repelled. Now let us suspend, by
means of a thread, a glass rod which has been electrified by rubbing
it with silk, and bring near it in turn another silk-rubbed glass rod
and a stick of sealing-wax rubbed with flannel. The two glass rods are
found to repel one another, whereas the sealing-wax attracts the glass.
If the experiment is repeated with a suspended stick of sealing-wax
rubbed with flannel, the glass and the sealing-wax attract each other,
but the two sticks of wax repel one another. Both glass and sealing-wax
are electrified, as may be seen by bringing them near the pith ball,
but there must be some difference between them as we get attraction in
one case and repulsion in the other.
The explanation is that the electric charges on the silk-rubbed
glass and on the flannel-rubbed sealing-wax are of different
kinds, the former being called positive, and the latter negative.
Bodies with similar charges, such as the two glass rods, repel one
another; while bodies with unlike charges, such as the glass and the
sealing-wax, attract each other. We can now see why the pith ball was
first attracted and then repelled. To start with, the ball was not
electrified, and was attracted when the rubbed glass or sealing-wax was
brought near it. When however the ball touched the electrified body it
received a share of the latter’s electricity, and as similar charges
repel one another, the ball was driven away.
The kind of electricity produced depends not only on the substance
rubbed, but also on the material used as the rubber. For instance,
we can give glass a negative charge by rubbing it with flannel, and
sealing-wax becomes positively charged when rubbed with silk. The
important point to remember is that there are only two kinds of
electricity, and that every substance electrified by rubbing is charged
either positively, like the silk-rubbed glass, or negatively, like the
flannel-rubbed sealing-wax.
If we try to electrify a metal rod by holding it in the hand and
rubbing it, we get no result, but if we fasten to the metal a handle
of glass, and hold it by this while rubbing, we find that it becomes
electrified in the same way as the glass rod or the sealing-wax.
Substances such as glass do not allow electricity to pass along them,
so that in rubbing a glass rod the part rubbed becomes charged, and
the electricity stays there, being unable to spread to the other
parts of the rod. Substances such as metals allow electricity to pass
easily, so that when a metal rod is rubbed electricity is produced,
but it immediately spreads over the whole rod, reaches the hand, and
escapes. If we wish the metal to retain its charge we must provide
it with a handle of glass or of some other material which does not
allow electricity to pass. Dr. Gilbert did not know this, and so he
came to the conclusion that metals were non-electrics, or could not be
electrified.
Substances which allow electricity to pass freely are called
conductors, and those which do not are called non-conductors; while
between the two extremes are many substances which are called partial
conductors. It may be said here that no substance is quite perfect in
either respect, for all conductors offer some resistance to the passage
of electricity, while all non-conductors possess some conducting
power. Amongst conductors are metals, acids, water, and the human
body; cotton, linen, and paper are partial conductors; and air, resin,
silk, glass, sealing-wax, and gutta-percha are non-conductors. When a
conductor is guarded by a non-conductor so that its electricity cannot
escape, it is said to be insulated, from Latin, _insula_, an island;
and non-conductors are also called “insulators.”
So far we have mentioned only the electric charge produced on the
substance rubbed, but the material used as rubber also becomes
electrified. The two charges, however, are not alike, but one is always
positive and the other negative. For instance, if glass is rubbed with
silk, the glass receives a positive, and the silk a negative charge.
It also can be shown that the two opposite charges are always equal in
quantity.
The two kinds of electricity are generally represented by the signs +
and -, the former standing for positive and the latter for negative
electricity.
The electricity produced by rubbing, or friction, is known as Static
Electricity; that is, electricity in a state of rest, as distinguished
from electricity in motion, or current electricity. The word static is
derived from a Greek word meaning to stand. At the same time it must
be understood that this electricity of friction is at rest only in the
sense that it is a prisoner, unable to move. When we produce a charge
of static electricity on a glass rod, by rubbing it, the electricity
would escape fast enough if it could. It has only two possible ways
of escape, along the rod and through the air, and as both glass and
air are non-conductors it is obliged to remain at rest where it was
produced. On the other hand, as we have seen, the electricity produced
by rubbing a metal rod which is not protected by an insulating handle
escapes instantly, because the metal is a good conductor.
When static electricity collects in sufficient quantities it discharges
itself in the form of a bright spark, and we shall speak of these
sparks in Chapter III. Static electricity is of no use for doing useful
work, such as ringing bells or driving motors, and in fact, except
for scientific purposes, it is more of a nuisance than a help. It
collects almost everywhere, and its power of attraction makes it very
troublesome at times. In the processes of textile manufacture static
electricity is produced in considerable quantities, and it makes its
presence known by causing the threads to stick together in the most
annoying fashion. In printing rooms too it plays pranks, making the
sheets of paper stick together so that the printing presses have to be
stopped.
Curiously enough, static electricity has been detected in the act of
interfering with the work of its twin brother, current electricity. A
little while ago it was noticed that the electric incandescent lamps in
a certain building were lasting only a very short time, the filaments
being found broken after comparatively little use. Investigations
showed that the boy was in the habit of dusting the lamp globes with
a feather duster. The friction set up in this way produced charges
of electricity on the glass, and this had the effect of breaking the
filaments. When this method of dusting was discontinued the trouble
ceased, and the lamps lasted their proper number of hours.