THE ELECTRIC TELEGRAPH.
The engineering and philosophical details of this important instrument
have grown to such formidable dimensions, that any attempt (short of
devoting the whole of these pages to the subject) to give a full account
of the history and application of the instrument, the failures and
successes of novel inventions, and the continued onward progress of this
mode of communication, must be regarded as simply impossible, and
therefore a very brief account of the _principle_ only will be attempted
in these pages.
For the complete history of the discovery and introduction of the
principle of the Electric Telegraph the reader is referred to the
Society of Arts Journal (Nos. 348-9, vol. viii.), where it is stated
that it is _half a century_, dating from August, 1859, since the first
galvanic telegraph was made. "It was the Russian Baron Schilling's
electro-magnetic telegraph which, without its being known to be his, was
brought to London, and caused the establishment of the first practically
useful telegraph lines, not only in Great Britain, but in the world."
Dr. Hamel says: "The small sprout nursed on the Neva, which had been
exhibited on the Rhine, and thence brought to the Thames, grew up here
to a mighty tree, the fruit-laden branches of which, along with those
from trees grown up since, extend more and more over the lands and seas
of the Eastern hemisphere, whilst kindred trees planted in the Western
hemisphere have covered that part of the world with their branches, some
of which will, ere long, be interwoven with those in our hemisphere."
The first telegraph line in England was constructed by Mr. Cooke from
Paddington along the Great Western Railroad to West Drayton in 1838-39;
and it must be remembered that it was in February, 1837, that Mr. Cooke
first consulted Professor Charles Wheatstone, having previously visited
Dr. Faraday and Dr. Roget, and on the 19th November, 1837, a partnership
contract was concluded between Messrs. Cooke and Wheatstone.
To the distinguished philosopher, Professor Wheatstone, the merit of the
ingenious construction of the vertical-needle telegraph is due; whilst
Mr. Cooke's name will always be associated with the practical
establishment of the first telegraph lines in England. The first line in
the United States, from Washington to Baltimore, was completed in 1844,
being arranged and worked by Professor Morse.
In British India, in April and May, 1839, the first long line of
telegraph, twenty-one miles in length, and embracing 7000 feet of river
surface, was constructed by Dr. (now Sir William) O'Shaughnessy.
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The construction of the electric telegraph may be considered under three
heads:
1st. The Battery, _the motive power_.
2nd. The Wires, _the carriers of the force_.
3rd. The Instruments to be worked--_the bell_ and the _needle
telegraph_.
THE BATTERY.
The construction and rationale of the batteries generally in use have
been explained in another part of this work; those used for telegraphic
purposes consist of one or more couples, of which zinc is one, the
second being copper, silver, platinum, or carbon. Each couple is termed
an element, and a series of such couples a _battery_.
The batteries employed chiefly on the English lines consist of a plate
of cast-zinc four inches square and 3/16ths of an inch thick, attached
by a copper strap one inch broad to a thin copper plate four inches
square. The zinc is well amalgamated with mercury. Twelve of these
couples are arranged in a trough of wood, porcelain, or gutta-percha,
divided by partitions into twelve water-tight cells, 1¼ inch wide.
The zinc and copper preserve the same order and direction throughout,
and when arranged, the trough is filled with the finest white sand, and
then moistened with water previously mixed with five per cent. by
measure of pure sulphuric acid. This mode of applying the acid is the
clever practical improvement of Mr. Cooke, and prevents any
inconvenience from the spilling of the acid, and at the same time
renders the battery quite portable. The voltaic arrangement thus
prepared is found to remain in action for several weeks, or even months,
with the occasional addition of small quantities of acid, and answers
well for working needle telegraphs in fine and dry weather. In fogs and
rains, at distances exceeding 200 miles at most, their action is not so
perfect, and a vast number of couples must be employed, 144 to 288 being
frequently in use. In France, Prussia, and America, sand batteries do
not appear to answer, and Daniell's arrangement is preferred. Sixty
couples suffice in France for some of the long lines--viz., from Paris
to Bordeaux, 284 miles; Paris to Brussels, 231¼ miles; and in fact,
the advantages of the Daniell's battery have become so apparent, that
they are now being used on English lines. In Prussia, Bunsen's carbon
battery is much used; in India, a modification of Grove's battery is
preferred, the zinc being acted upon by a solution of common salt in
water. Two of these elements were found sufficient to work a line of
forty miles totally uninsulated, and including the sub-aqueous crossing
of the Hooghly River, 6200 feet wide.
The continual energy of the battery, whatever may be its construction,
depends on the circulation of the electricity, the object being to pass
the force from the positive end of the series through the wires, back
again to the negative extremity of the voltaic series.
The wire (the carrier of the force) must be continuous throughout,
unless, of course, water or earth forms a part of the endless conducting
chain.
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THE CONDUCTING WIRES.
These roads for the electricity may be of any convenient metal, and the
one preferred and used is iron, which is well calculated from its great
tenacity (being the most tenacious metal known) and cheapness to convey
the electricity, although it is not such a good conductor as copper, and
offers about six times more resistance to the flow of the current than
the latter metal. The wire does not appear to be made of iron, because
it is galvanized or passed through melted zinc, which coats the surface
and defends it from destructive rust, at the same time does not destroy
its valuable property of tenacity or power of resisting a strain. About
one ton of wire is required for every five miles, and to support this
weight, stout posts of fir or larch are erected about fifty yards apart,
and from ten to twenty-five feet high. At every quarter mile, on many
lines, are straining-posts with ratchet wheel winders, for tightening
the wires. On some of the lines the wires are attached to the posts by
side brackets carrying the insulators invented by Mr. C. V. Walker,
which are composed of brown salt-glazed stoneware of the
hour-glass shape, as shown in the drawing. (Fig. 208.)
[Illustration: Fig. 208. Walker's insulator.]
There are some objections to the hour-glass insulators, and they have
been modified by Mr. Edwin Clark, [Page 221] who employs a very strong
stone-ware hook open at the side, so that the wire can be placed on the
hook without threading, and the hooks can be replaced in case of
breaking, without cutting the telegraph wire, which is securely fastened
to each insulator by turns of thinner wire. An inverted cap of zinc is
used to keep the insulator dry. (Fig. 209.)
[Illustration: Fig. 209. Clark's insulator.]
In India the conductor is rather a rod than a wire, and weighs about
half a ton per mile; it is erected in the most substantial manner, and
many miles of the rod are supported on granite columns, other portions
on posts of the iron-wood of Arracan, or of teak.
The number of wires required by the electric telegraph often puzzles the
railway traveller, and people ask why so many wires are used on some
lines and so few on others? The answer is very simple: they are for
convenience. Two wires only are required for the double needle
telegraph, and one for the single needle instrument. But as so many
instruments are required at the terminal stations, an increased number
of wires, like rails for locomotives, must be provided; thus, on the
Eastern Counties, seven wires are visible, and are thus employed. The
two upper wires pass direct from London to Norwich; the next pair
connect London, Broxbourne, Cambridge, Brandon, Chesterfield, Ely; the
third pair all the small stations between London and Brandon; and the
seventh wire is entirely devoted to the bell.
If the earth was not a conductor of electricity, and employed in the
telegraphic circuit, four wires would be required for the double needle
telegraph, and two for the single instrument. To understand this, let us
suppose a battery circuit extending from Paddington to the instrument at
Slough, and the wire returning from Slough to Paddington, it is evident
that one wire would take the electricity to Slough, and the other return
it to London, as in the diagram below. (Fig. 210.)
[Illustration: Fig. 210. A. The battery. B. The instrument. The arrows
show the passage of the electricity to the single needle telegraph
instrument by one wire, and the return current by the other.]
If the whole of the return wire is cut away except a few feet at each
end, which are connected by plates of copper with the damp earth, the
current not only passes as before, but actually has increased in
intensity, and will cause a much more energetic movement of the needle
in the telegraph instrument. (Fig. 211.) These plates are called "_Earth
Plates_;" and Steinheil, in 1837, was the first who proved that the
earth might perform the function of a wire.
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[Illustration: Fig. 211. A. The battery. B. The instrument. C. Earth
plate at Slough. D. Earth plate at London. The arrows show the direction
of the electric current.]
It must be obvious that a message may be received at any station without
a battery, but in order to be able to return an answer, every station
must have its own battery.
Ingeniously-constructed lightning-conductors are attached to the posts
which carry the wires, so that in case of a storm, the natural
electricity is conveyed to the earth, whilst the voltaic electricity
artificially produced pursues its own course without deviation.
Protectors are also required for the instruments at the stations, and
the plan devised by Mr. Highton is thus described by the inventor:--
"A portion of the wire circuit--say for six or eight inches--is
enveloped in blotting-paper or silk, and a mass of metallic filings, in
connexion with the earth, is made to surround it. This arrangement is
placed on each side of the telegraph instrument at a station. When a
flash of lightning happens to be intercepted by the wires of the
telegraph, the myriads of infinitesimally fine points of metal in the
filings surrounding the wire at the station, on having connexion with
the earth, at once draw off nearly the whole charge of lightning, and
carry it safely to the earth."
THE INSTRUMENTS TO BE WORKED--THE BELL AND THE TELEGRAPH.
The bell or alarum resembles in construction that of an ordinary clock,
and is in fact a piece of clockwork wound up and ready to ring a bell,
when the _detent_ or preventive is removed. The detent is connected with
a piece of soft iron placed before an electro-magnet, and directly the
current passes, the electro-magnet attracts the soft piece of iron
attached to a perpendicular lever which the bell-crank lever rests upon;
the detent is removed, and the bell rings, and again stops when the
current of electricity ceases to pass.
One of the most simple alarum clocks is a common American clock, wound
up daily. A small electro-magnet surrounded with thick wire is placed
below a moveable piece of tinned iron, so that when this is attracted,
the fly of the clock is released, and its bell tolls unceasingly while
[Page 223] the magnet is excited. This arrangement is employed by Sir W.
O'Shaughnessy in the Indian telegraph system. (Fig. 212.)
It will readily be comprehended from this description that the alarum is
sounded by ordinary mechanism, and that the duty of the current of the
electricity is simply comprised in the act of removing the lever and
liberating machinery, which may be large or small; and if it were
thought necessary, the bells of the great clock-tower of the Houses of
Parliament, which chime the quarters, or even "Big Ben" himself (when
his constitution is restored), could be rung by a person at York or
Edinburgh, supposing wires, batteries, and a powerful electro-magnet
with a detent mechanism for the bells, were properly arranged and
connected with the clockwork.
[Illustration: Fig. 212. A. The soft iron tinned, which is attracted to
the electro-magnet B, and liberates the detent.]
In certain cases, Mr. Charles V. Walker states that a single and
distinct wire is used for the bell only, with his special mechanism,
called the _ringing key_. If the bell was always on the same wire as the
needle-coil, the bell would not only call the attention of, but
seriously annoy the clerk (unless, of course, he happened to be a very
deaf person) by its ringing whilst he was reading the signals of the
needle. The nuisance is prevented by what is termed _joining over_ or
making the _short circuit_--in fact, by providing for the current a
shorter and much more capacious road to the needle coil than by going
through that of the bell-magnet, which is made with very fine wire; and
the control of the short circuit is put in the hands of the clerk.
COOKE AND WHEATSTONE'S DOUBLE NEEDLE TELEGRAPH.
The principle of this instrument, as already explained, is involved in
the elementary experiment of Oersted--viz., the deflection of a magnetic
needle from the inside of a coil of wire conveying a current of
electricity, and as it is difficult to give a good description and
drawing of the interior of the instrument that can really be understood,
it may be sufficient to state that the handles give the operator the
power of reversing the current of electricity, so that the needles are
deflected with the utmost certainty to [Page 224] one side or the
other, either separately or simultaneously. (Fig. 213.)
[Illustration: Fig. 213. The letters of the alphabet, figures, and a
variety of conventional signals, are indicated by the single and
combined movements of the needles on the dial. The left-hand needle
moving once to the left indicates the +, which is given at the end of a
word. Twice in the same way, A; thrice, B; first right, then left, C;
the reverse, D. Once direct to the right, E; twice, F; thrice, G. In the
same order with the other needle for H, I, K, L, M, N, O, P. The signals
below the centre of the dial are indicated by the parallel movements of
both needles simultaneously. Both needles moving once to the left
indicate R; twice, S; thrice, T. First right, then left with both, U;
the reverse, V. Both moving once to the right, W; twice, X; thrice, Y.
The figures are indicated in the same way as the letters nearest to
which they are respectively placed. To change from letters to figures
the operator gives H, followed by the +, which the recipient returns to
signify that he understands. If, after the above signs (H and +) were
given, C R H L were received, 1845 would be understood. A change from
figures to letters is notified by giving I, followed by the +, which the
recipient also returns. Each word is acknowledged. If the recipient
understand, he gives E; if not, the +, in which case the word is
repeated. Attention to a communication by this instrument is called by
the ringing of a bell (of any size), which is effected through the
agency of an electric current. The upper case contains the bell.]
Sir W. O'Shaughnessy, in his excellent work on the electric telegraph in
British India, gives a description of a telegraphic instrument of
remarkable simplicity, which is successfully employed in India, and is
[Page 225] highly spoken of by Mr. E. V. Walker and other gentlemen
practically acquainted with the working of telegraphs. It consists of a
coil of fine wire on a card or ivory frame, a magnetic needle with a
light index of paper pasted across it; two stops of thin sheet lead to
limit the vibrations of the index; a supporting board eight inches
square, and a square of glass in a frame of wood, or a common glass
tumbler placed over it as a shade, to prevent the index being moved by
currents of air. It is stated that the office boys, with the assistance
of a native Indian carpenter, make up these telegraphs at a price not
exceeding two shillings each.
In England of course they would be more expensive; but the simplicity
and perfection of the arrangement are so much to be commended that we
give the details for the benefit of those boys who might wish to
establish a telegraph on a small scale for amusement.
THE FRAME.
This is a piece of mahogany eight inches square and one inch thick, with
a hollow groove cut in its centre two inches and a half long, half an
inch wide, and a quarter of an inch deep; a ledge of the same wood one
inch wide and half an inch deep surrounds the frame, leaving the inner
surface seven inches square; this is stained black with ink to make the
motions of the index more conspicuous.
THE COIL.
This consists of fifty feet of the finest silk-covered copper wire wound
on a frame of card two inches long, half an inch broad, three-eighths
deep in the open part.
An edge or flange of card, three-eighths of an inch wide, is attached to
it at each side to keep the wire in its place. The frame may be of thin
wood or ivory, and the winding of the wire commences at the lower left
corner, and it is coiled from left to right, as the hands of a watch
would move in the same plane. (Fig. 214.)
[Illustration: Fig. 214. The coil.]
Two inches of each end of the coil wire are now stripped of their silk
covering by being rubbed with sand-paper. The coil is mounted in the
frame by inserting its lower edge or flange in the groove, so that the
lower part or floor of the inside of the coil is level with that of the
[Page 226] frame, as shown below, and it is now ready to receive the
magnetized needle. (Fig. 215.)
[Illustration: Fig. 215. The coil fitted into frame.]
THE NEEDLE.
This is one inch long, one-twelfth of an inch wide, of the thinnest
steel, and fitted with a little brass cap turned to a true cone to
receive the point on which it is balanced. These needles are of hard
tempered steel, and are magnetized by a single contact with the poles of
an electro-magnet or other ordinary powerful magnet.
The magnet is now to be balanced on a steel point one-eighth of an inch
high; these are nipped off with cutting pliers from common sewing
needles, and soldered into a slip of thin copper three inches long, half
an inch wide. (Fig. 216.)
[Illustration: Fig. 216. A. The needle. B. The point on the slip of
copper.]
As the north end of the needle will be found to dip, it is advisable to
counteract this by touching the south end with a little shell-lac
varnish, which dries rapidly, and soon restores the needle to a perfect
equilibrium.
The needle is completed for use by fixing to it an index of paper (cut
from glazed letter paper) two inches long, tapering from one-eighth of
an inch to a point, and fastened at right angles on to the needle with
lac varnish, so as to be truly balanced, and pointing the sharp end to
the east, when the needle placed on the point settles due north and
south, its north pole being opposite the observer's right hand, the
observer facing west. (Fig. 217.)
[Illustration: Fig. 217. The needle with the paper index.]
[Page 227]
The coil frame is placed north and south, and the needle is now
introduced by sliding the end of the slip of copper into the opening in
the frame.
To limit the vibrations of the paper index a _stop_ is placed at each
side. The stops are made of a strip of thin sheet-lead or copper, a
quarter of an inch broad, one inch and a half long, and turned up at a
right angle, so that one inch rests on the board and half an inch is
vertical. For ordinary practice these stops are placed each at half an
inch from the index.
The telegraph is placed in a box, which may have a piece of
looking-glass in the lid, so that the readings can be taken with the
needle in the vertical instead of the horizontal position, if required.
(Fig. 218.)
[Illustration: Fig. 218. Box containing the telegraph, with the
looking-glass in the lid. A small steel magnet is placed on or near the
frame, if required, the south pole of this magnet being opposite to the
north pole of the needle in the telegraph coil. The bar is four inches
long, half an inch broad, three-sixteenths of an inch thick, and it is
only used to counteract any local deviation which may arise in using the
instrument with miles of wire. It would not be required under ordinary
circumstances. The alphabet used is shown to the left.]
The ends of the fine wire of the telegraph coil are joined on to the
wires from the _reversing_ instrument, and this is connected with a
voltaic series of one or more elements, so that by the employment of the
reverser the needle is caused to move right or left at pleasure. The
[Page 228] white paper index on the black ground can be followed with
the greatest certainty, and Sir W. O'Shaughnessy states that with this
instrument a telegraph clerk may read at the rate of twenty words per
minute with a double needle wire, being equal to forty words per minute.
THE REVERSER
consists of a block of wood, two inches and a half square, in which four
hollows, half an inch deep, are cut, and these hollows are joined
diagonally by copper wires let into the substance of the wood, and most
carefully insulated from each other by melted cement, but exposing a
clean metallic surface in each cell, which is filled with mercury. (Fig.
219.)
[Illustration: Fig. 219. Block of wood with four holes; the positive
terminal is connected with the holes A and B, the negative with C and D;
the hollows are filled with mercury. T T are the wires from the
telegraph box, and it is obvious that by dipping them alternately into C
B and A D the current is reversed, and the needle deflected right or
left at pleasure.]
In practice a more elaborate reverser is employed, but to demonstrate
the principle the simple block above described is quite sufficient.
With the telegraph placed at the top of a house, or in a distant
cottage, and a single cell of Grove's battery, or at most two, for any
short distances, with the reverser, messages may be passed with great
rapidity from the bottom of the house to the top, or from a mansion to
the lodge, it being understood that a battery, reverser, and telegraph,
are required at both places where messages are received and _answered_;
but if no answers are required, the battery and reverser are placed at
one end of the wire in the house, and the telegraph at the other
extremity in the cottage, and earth plates may be arranged to return the
current, or another wire used for that purpose.
Whilst lauding to the utmost the invention of the electric telegraph, we
must remember "there is nothing new under the sun," and that after all
Nature claims the _principle_ of telegraphing, and with the silent
gesture, the speaking eye, interpreted and answered by others, she
proclaims herself to be the originator of communication by signs.
Whilst [Page 229] the language of flowers, and the mournful
requirements of the deaf and dumb in the use of the finger alphabet,
show how readily man has adopted the important principle, till he has
brought it to the highest state of perfection in the electric telegraph.
When the telegraph was first adopted on the Great Western Railway, the
most ridiculous ideas were formed of its capabilities, and many persons
firmly believed that the wires were used for the purpose of dragging
letters and different articles from station to station. "Wife," said a
man, looking at the telegraph wires, "I don't see, for my part, how they
send letters on them wires, without tearin' 'em all to bits." "Oh, you
stupid!" exclaimed his intellectual spouse; "why, they don't send the
paper: they just send the writin' in a _fluid_ state."
[Illustration: Fig. 220. One of the ideas of telegraphic
communication.]
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