Thomas Dixon Lockwood.

Electricity, magnetism, and electric telegraphy; a practical guide and hand-book of general information for electrical students, operators, and inspectors online

. (page 1 of 27)
Online LibraryThomas Dixon LockwoodElectricity, magnetism, and electric telegraphy; a practical guide and hand-book of general information for electrical students, operators, and inspectors → online text (page 1 of 27)
Font size
QR-code for this ebook









MAY 5 1894 ' '*<>

x - , /x -,
No<5<y~r~rj./ . No. ' .












Copyrighted, 1883,




ELECTRICITY is pre-eminently a science of the nine-
teenth century.

We cannot even at this late day say that we know
what electricity is ; and within a comparatively recent
period even its manifestations and phenomena were fa-
miliar to a relatively small class, composed chiefly of
college professors and scientific lecturers.

Few of the class which was entrusted with the man-
agement of its practical applications viz., telegraphers
and electro metallurgists had any scientific knowledge
of its laws, or, in fact, anything but a mechanical and
empirical knowledge of the manipulation of the tele-
graph instrument and the electrolyzing battery.

This state of things has, however, passed away, and
electricity has become the favorite, most promising, and
most important scientific study of that section of the
human race which, under the title of inventor, aspires
to achieve fame or fortune, or both, by the work of its
own brains.

During the last decade we have seen such wonderful
developments in electricity and electro-magnetism that
while on the one hand we can scarcely conceive of any-
thing which cannot be done by these agencies, on the
other hand we are almost compelled to believe that
there is little more left for electricity to achieve.

It is true that for many of the greatest discoveries


and inventions which have been made we are indebted
to persons who have not been practical electricians, but
it is also true that it is to the practical electrician we
turn when these discoveries are to be utilized ; and it is
to be regretted that among the thousands of our tele-
graphers and telephonists so few are to be found capa-
ble of assuming an important trust, and of practically
and ably filling important positions in the many appli-
cations of electricity.

A general knowledge of the theory and practice of
electricity and magnetism is, then, a most desirable and
valuable acquirement for all who are in any way, or
who intend to be, connected with the practical applica-
tion of either science.

And this desirability, and the knowledge that but few
of the many books written upon the subject are fitted
for the self-helper, who has to struggle against many
difficulties, notably that of neglected early education,
forms the excuse of the author for inflicting another
book upon the electrical public.

Imperfect as this volume is in many ways, such a one
would have been a great help to the author had he in
his earlier years had the fortune to stumble across it,
and it is his earnest hope that its contents will in some
measure aid those for whom it is written those who
desire to obtain a knowledge of electricity and magnet-
ism and their possibilities, but who are unable to obtain
the advantages of a college or institution course and
enable them to answer for themselves the innumerable
questions which constantly force themselves upon the
thinking mind when daily occupied in the utilization
of these mysterious agencies. If the readers of this
work learn but one tithe as much of the various sub-


jects treated of as the author has while working upon
it, they will be benefited, and will perhaps be more
ready to digest the more solid contents of such standard
books as Culley's " Hand-book of Practical Telegraphy "
and Fleeming Jenkin's " Electricity and Magnetism/'

The author has endeavored to put the information in
as lucid and concise form as is consistent with accuracy,
and to combine brevity with completeness. How he
has succeeded is for others to judge. A liberal use
has been made of the electrical text-books, and of the
literature relating to kindred subjects, also of the cur-
rent electrical journals of the day ; and valuable infor-
mation has especially been obtained from the well-
known " Modern Practice of the Electric Telegraph " by
Mr. Pope; Culley's " Hand-book of the Electric Tele-
graph" ; Prescott's " Electricity and the Electric Tele-
graph" ; Preece and Sivewright's " Telegraphy" ; and
" Elementary Lessons in Electricity and Magnetism,"
by Silvanus P. Thompson.

The acknowledgments of the author are also due to
his friend Frank L. Pope for his constant advice and
encouragement during the preparation of the work.


Dept. [email protected] k Sag.



Electricity generated by Friction, . . . . . .9

Voltaic Electricity, . . .22

Thermo- Electricity, . . . 36

Earth-Currents and Earth -Batteries, 41

Magnetism Electro-Magnetism and Electro-Magnets, . . 43


Magneto -Electricity, and Magneto and Dynamo-Electric Ma-
chines, 59

Induction-Coils and Condensers, . 80

Definitions of Electrical Properties, Terms, and Units, . . 89

Electrical Measurements, 98

Principles of Telegraphy exemplified in Different Systems, . 130

Voltaic Circuits, 142




Line Construction, . 153

Subterranean and Submarine Conductors, .... 184

Office- Wires, and Fittings and Instruments, .... 192

Adjustment and Care of Telegraph Instruments, . ... 222

Circuit Faults and their Localization, 231

Multiple Telegraphs, 242

Miscellaneous Applications of Electricity Electric Lighting, . 266

Electro-Metallurgy, 281

Electric Bells, 286

The Telephone, 299

Electro-Therapeutics, 318


Other Applications of Electricity : Electric Clocks Time-Balls
Alarms Blasting Transmission of Power Electrical
Storage, 323

Odds and Ends, 351




1. What is electricity ?

Electricity is one of the peculiar forces of nature ;
it is as universal in its effects as its kindred forces, light
and heat, and is in many respects analogous to them.
It has been common to speak and write of electricity as
if it were a fluid, capable of flowing as a current. It
is, however, now usually considered by scientists to be
simply a particular form of energy,* which causes the
infinitesimal particles of matter to alter their positions
in regard to one another.

2. From whence does electricity derive its name ?

It was observed in ancient times that when amber f
was rubbed it acquired a power of attracting and re-
pelling light bodies, such as hair and feathers. This
power afterwards came to be called electricity, from
" electron," the Greek word for amber.

3. Why has it become customary to speak of electricity as if
it were a fluid, and consequently subject to the laivs of fluids ?

Because for many years it was in fact thought to
be a fluid. The fluid theory was first propounded by

* Energy in a mechanical sense may be defined as capacity for performing work
or for moving against resistance.

t Amber is a resin of yellowish color resembling copal, found as a fossil. It takes
a fine polish and is used for ornaments and also as a basis for a superior quality of



Du Fay, of France, who supposed that there were two
electric fluids, naturally commingled and neutralized,
which universally pervaded all matter. Dr. Benjamin
Franklin proposed a second hypothesis, ascribing all
observed electrical effects to one fluid, which, as in the
former case, was supposed to pervade all bodies. Ac-
cording to Franklin's theory, it was supposed that the
electrical equilibrium or balance constituting the natural
state of matter was disturbed by friction, and that one
of the two bodies brought near to each other, was, so
to speak, over- saturated with electricity, while the other
was left under-saturated. This also explains the origin
of the terms plus and minus as applied to opposite
electrical states or conditions. As the terms which have
come to be adopted in speaking of electricity and its
properties are nearly all based on the foregoing theo
ries, and have in this manner become familiar to men
of science everywhere, it has by common consent been
considered unwise as well as unnecessary to change

4. What is the simplest method of producing electricity ?

By rubbing together two suitable substances, such,
for example, as a tube or rod of glass and a woollen
cloth. Electricity so produced is called frictional elec-

5. Is not electricity produced in different states or conditions f
Yes, Certain substances, such as sealing-wax and

resin, when rubbed by a woollen cloth, exhibit what is
sometimes called resinous electricity ; while glass or
other vitr.eous bodies, when rubbed with the same cloth,
exhibit what is called vitreous electricity. These names
are, however, somewhat unsuitable, as they imply that
the same substances always produce the same kind of
electricity, irrespective of conditions ; whereas a tube of
glass, when rubbed by the fur of a cat, produces the same
kind of electricity as sealing-wax. The terms positive
and negative are less objectionable, and are still very
generally employed.


We may, therefore, call the electricity produced by
rubbing glass with a woollen cloth positive, and denote
it, for the sake of brevity, by the sign plus, or + ; and
that produced on a stick of sealing-wax, when rubbed,
negative, and denote it by the sign minus, or .
These terms, however, must not be understood to indi-
cate that one electricity is more powerful or potent than
the other ; they are purely arbitrary, and merely used
for the sake of distinction, to denote that the two elec-
trical states are opposite in character. Both kinds of
electricity are always produced at the same time and in
equal quantities, one of the bodies rubbed exhibiting
plus and the other minus electricity.

6. What is an electrical conductor ?

Conductors are those bodies and substances which
permit electricity to freely diffuse itself through them.
All the known metals are good conductors. Many
non -metallic substances are also conductors. The inhe-
rent conducting power of bodies depends largely upon
conditions ; for instance, ordinary water when in liquid
form is a conductor, but when frozen becomes a non-
conductor. Iron, when cold, is a good conductor ; when
hot, a very poor one.

7. What is an insulator, or non-conductor ?

Bodies which offer very great resistance to the pas-
sage of electricity, such as dry air, paraffine, gutta-
percha, india-rubber, and glass, are called non-conduc-
tors, or insulators, from insvla, an island. There is no
absolute distinction between insulators and conduc-
tors. The difference is in degree only, all bodies be-
ing, strictly speaking, conductors in a greater or less
degree, the worst conductors being the best insulators.
Hence a list of conductors, arranged in the order of their
conducting power, becomes, if read backward, a list of
insulators, and in the middle of the list the conductors
and insulators merge insensibly into each other.


8. Define the terms "electric" and "non-electric" which are
sometimes applied to substances.

It was formerly considered that insulators were the
only bodies upon which electricity could be excited,
hence they were also denominated electrics ; while the
conductors, such as the metals, were called non -electrics.
This supposition was, however, an erroneous one, as,
when properly insulated, the most perfect conductors
can be electrified. The distinction between electrics and
non-electrics is, therefore, no longer admissible, although
the terms are still frequently used in works on electri-

9. What is an electroscope ?

An instrument for indicating the presence and char-
acter of electricity. A gold-leaf electroscope consists
A of a glass vessel, B, into

which is inserted a metallic
rod terminating in two
gold leaves, ft, and sur-
mounted by a metallic
plate or ball, C. If the
plate is touched by an
electrified body, A, the ex-
citement passes down to
the leaves and causes them
to repel each other, or to
diverge. An instrument
provided with means of
measuring the amount of
divergence, and thereby measuring the amount of elec-
tricity present, is called an electrometer.

10. What is an electrical machine f

It is an apparatus for obtaining large quantities of
electricity, usually by the friction of an extended sur-
face of some suitable non-conductor, such as glass or
hard rubber.

In order that glass may be conveniently subjected to
friction for the development of electricity, it is formed

Fig. 1. The Electroscope.



into a circular plate, P, mounted on an axis supported
on a wooden frame, O, and revolved by a crank, M, while
cushions or rubbers, F, press against its surface. To
equalize the pressure of the rubbers they are placed at
the top and bottom, and on both sides, of the glass.
In front of the plate are two rods of metal, C, supported
by glass legs. These are called the prime conductors,

Fig. 2. The Electrical Machine.

and are provided with branches, which are studded with
sharp points and bent round the glass plate.

When the plate is revolved by means of the crank, by
reason of the friction against the cushions it becomes
positively electrified ; negative or minus electricity be-
ing at the same time produced in the rubber. When
the plus electricity, carried round by the rotation of the


plate, arrives opposite the points of the prime conductor,
it acts inductively thereon, repelling its plus electricity
to the distant end and attracting minus electricity to
the end nearest the machine. The points then discharge
the minus electricity so accumulated towards the plus
charge on the revolving plate, which is thus neutralized,
and the neutralized portion of the plate arrives at the
rubber in a neutral state and ready once more to be
excited. If now any electrically neutral substance be
brought near to the distant end of the prime conductor,
minus electricity will be abstracted from it and will
pass along the conductor to keep up the supply neces-
sary for a continuous neutralization of the excited plate;
hence the prime conductor, and any conductor attached
or brought near thereto, will acquire a surplus of plus
electricity, or become charged, and this charge may be
conducted away or collected in Ley den jars at will for
experimental purposes.

If it is desirable that the minus electricity be also col-
lected, the rubber is supported upon a nori- conducting
stand and provided at the back with a metallic knob.

But generally, the negative or minus electricity is al-
lowed to pass to earth by connecting the rubbers, by
means of a chain or wire, D, with the earth.

In charging a Ley den jar, if the rubbers are connected
to earth, the outside of the jar must also be connected
with the earth ; but if the outside of the jar and the
rubbers be connected together it is not essential that
either should be attached to earth.

Another common form of the electrical machine is the
cylinder. The chief distinction between this and the
plate machine lies in the use of a cylinder of glass in-
stead of a plate.

11. What is an electrophorus ?

It is an instrument, invented by Volta, which is an
exceedingly convenient source of electricity when re-
quired in comparatively small quantities. It consists of
three essential elements : 1st. A cake, B, of some resinous


material easily excited by friction. 3d. A conducting-
plate, which is a metallic dish into which the resinous
composition is poured, and which is connected to earth.
3d. A disc of metal, or of wood covered with tin-foil. A,
and provided with an insulating handle.

It is very convenient to so arrange the electrophorus
that the cover, when placed on the resinous plate, comes
into metallic connection with the metal dish below, and
thereby, of course, with the earth. The resinous cake is
excited negatively by rubbing, and the metal plate laid

Fig. 3. The Electrophorus.

upon it ; on lifting it away it is found to be positively
electrified and will give a spark. It may then be re-
placed on the lower plate and the process indefinitely

The upper plate does not receive its charge direct from
the excited resin, but by induction, the negative charge
on the resin attracting the positive and repelling the
negative electricity of the upper plate which, by means
of the metal connection with the lower plate or by the
touch of the finger as in the figure, escapes to earth.
Instead of pouring a resinous composition into the


dish, a flat piece of vulcanite may be fixed therein to
subserve the same purpose.

12. Have machines for furnishing large quantities of electri-
city been constructed on the principle of the electrophorus 1

Yes, such machines have been constructed by several
physicists ; and one that of Holtz has come into very
general use. In it, as in other machines of this class, a
small initial charge is given to a piece of varnished paper
fixed on a stationary portion of the machine.

This initial charge acts inductively and develops other
charges, which are conveyed by a rotating glass disc to
some other part of the machine, where they may either
increase by accumulative action the initial charge or
furnish the supply of electricity to a suitable collector ;
or the machine may be caused to perform both functions,
much upon the same principle as that of the dynamo-
electric machine. (See chapter vi.)

Like the Gramme and other continuous- current ma-
chines, it, too, is reversible ; and if a continuous supply
of both plus and minus electricities be supplied simul-
taneously to the opposite extremes of the machine, the
movable parts of the machine will rotate.

A Holtz machine may be made to furnish a continuous
current, the strength of which is dependent upon the
rate at which the movable part is rotated, becoming
greater when the rotation increases in speed.

13. What is the meaning of the words "static" and "dyna-
mic " ivhen applied to electricity f

They are derived from the Greek. The word
"static" conveys the idea of force at rest, and "dy-
namic" the idea of action or of force due to motion.
Electricity developed by friction is often called "stat-
ical," because it tends to remain quiescent on the bodies
whereon it is excited, or in fact wherever it is placed.

The word static, or statical, refers to the electrical
condition of bodies whereon electricity remains station-
ary. For instance, a Leyden jar may be charged, and
remain charged without requiring a continual supply to



Fig. 4.
Leyden Jar.

be poured in ; hence the electricity it is charged with
is called statical, or reposing, electricity. On the other
hand, voltaic electricity is frequently styled dynamical,
because the excitement arises in a constant stream, and
can hardly be said to exist if it is not continually
evolved, and in that condition it exercises or performs
work ; and statical electricity becomes transformed to
dynamical when in the act of discharge, or when pass-
ing from one body to another.

14. What is a Leyden jar, and whence does it derive
its name f

It is a device for the accumulation of elec-
tricity, and, described as simply as possible,
consists of a glass jar coated both inside and
out with tin- foil, except a few inches at the
top. Through the cork or insulating cover is
passed a brass rod with a knob on the end,
which is in electrical communication with the
inner coatings.
It was discovered in November, 1745, by Kleist, a
German ecclesiastic. The Leyden philosophers were
the first to state the conditions necessary for its suc-
cess, and hence it receiv-
ed the name Leyden jar.
The jar is charged by
bringing the knob near
to the prime conductor
of the electrical machine,
while the outer coating
is usually in electrical
communication with the
earth. When the knob
is brought into connec-
tion with the outside
coating of the jar a

flash of intense brightness, accompanied by a loud re-
port, immediately ensues, and the jar is said to be

Fig. 5. Discharge of a Leyden Jar.


15. WJiat does the term "dielectric" imply 1

The insulating substance which separates two con-
ducting surfaces, and thereby enables them to sustain
opposite electrical states, was by Faraday called a di-

The sheets of paraffined paper between the tin-foil
sheets of a condenser, constitute a familiar example of
a dielectric. All insulators are dielectrics, but the best
insulators are not always the best dielectrics.

The glass jar between the inside and outside coatings
of tin-foil is, in a Leyden jar, the dielectric.

16. What is an electric battery ?

When a great amount of surface is needed to store a
considerable quantity of electricity, a number of jais
are set in a box lined with tin -foil so as to connect all
the outer coatings together. Their inner coatings are
also connected by conductors joining all the knobs to
one central knob. This constitutes an electric battery.
It is charged and discharged like a single jar, and its
effect is much the same as would follow from one large
jar whose extent of coating was equal to the sum of
those which constitute the battery.

17. Does static electricity reside at the surface, or throughout
the substance of bodies ?

Electricity at rest, resides on the surface only of con-
ductors. This may be proved by enclosing an electri-
fied metallic sphere in two tight-fitting, non-electrified
hemispheres. If the hemispheres are quickly removed
and presented to an electroscope they will be found to
be electrified, while the sphere itself has lost its elec-

18. What may we understand by the word "induction"*
It is the name given to electrical or magnetic effects

produced in bodies to which the exciting force is not
directly applied, and may for general purposes be di-
vided into the following heads : 1st. Electro- static or
static induction is the influence which an electrified
body has on all conducting bodies in its immediate

Dept. Mech, Bug.


vicinity, even though it has not touched them, causing
them to exhibit signs of electrification. It is similar to
the power exerted by a magnet on pieces of iron which
may be near it. 2d. Dynamic or voltaic induction is
the power which a galvanic current has, when flowing in
a conductor, of inducing currents in neighboring con-

For example, should two wires be placed near each
other, parallel but not touching, one connected with a
battery by means of a circuit-closing key, the other to a
sensitive galvanometer, it would be seen that whenever
the circuit was closed by the key on the first wire, and a
current thereby caused to pass through it, the galvano-
meter attached to the second wire is deflected by a cur-
rent flowing in the opposite direction to the battery

The battery current is called the inducing or primary
current ; the current that deflects the galvanometer the
induced or secondary current. The induced current
lasts but for an instant. When, however, contact is
once more broken the needle is again deflected, but
this time the induced current flows in the same direction
as the primary current, and is, like the former current,

3d. Electro-magnetic induction is the power which an
electric current, traversing a conductor, has upon non-
inagnetized iron, which, under certain conditions, may
by its influence become converted into a magnet.

This power is the basis of one of the most universally
useful applications of electricity namely, the electro-

Online LibraryThomas Dixon LockwoodElectricity, magnetism, and electric telegraphy; a practical guide and hand-book of general information for electrical students, operators, and inspectors → online text (page 1 of 27)