Chapter XX: Galvanism (2)

For the sake of clearness, the diagram has been drawn with simple lines only. In the real needle-machine the construction is much more complicated; perspective drawings of it may be seen in Lardner’s “Electric Telegraph,” and numerous other works. In fig. 1, B is a single cell of a battery containing a plate of copper, C, and a plate of zinc, Z, immersed in sulphuric acid and water. H is the handle of the instrument, turning from left to right, and _vice versâ_, like the handle of a door, consisting of two pieces of brass insulated from each other by being inserted in an axis of ivory. To the ends of the two pieces of brass are fixed the wires, CW and ZW, leading from the copper and zinc ends of the cell respectively. Fixed on each side of the handle are two plates of metal, which may be called LP, the left plate, and RP, the right plate. They are connected with the needle wire, NW, which passes before and behind the magnetized needle, N, suspended perpendicularly on its axis, with its north pole upwards. As long as the wires, CW and ZW, remain insulated from each other, no current passes from the cell; but as soon as the handle, H, is turned, so that the copper end touches the left plate (fig. 2), and the zinc end touches the right, communication is established between the plates of the cell, and the current commencing at the copper passes along CW, the top half of H, into LP, along N W, travelling _up before_ and _down behind_ the needle, causing it to deflect to the observer’s left, according to the rule given above. Reaching RP, it passes downwards to the cell to Z, and so on to C, continuing its travels and keeping the needle deflected as long as the handle remains in contact with the plates. If it is required to deflect the needle to the right, the handle is turned to the right, bringing its copper end in contact with the right plate, causing the current to travel in the opposite direction. By following the current from the copper to the zinc, as indicated by the arrows in fig. 3, it will be seen that it now travels _up behind_ and _down before_ the needle, deflecting it to the observer’s right. Thus, by causing a current of voltaic electricity to pass alternately _up before_ and _down behind_, and _up behind_ and _down before_, the needle is moved to the left or the right at will. The way in which the current is made to act on a distant needle is now simple. The following figure (fig. 253) shows the arrangement. The left portion of the figure represents an instrument at London, that on the right an instrument at York. The needle-wire, instead of being continued directly to the zinc plate of the battery, passes away from the needle over poles to York, where it joins an instrument similar in all respects to that at London. It passes similarly before and behind a magnetized needle, joining the right plate of the instrument. As long as the two plates are unconnected, no current can pass. The current is therefore completed by a contrivance which may be represented by the semicircular piece of metal, K. In practice the two plates or springs, which, when not in use, are always pressed against the connector, K, which is a cross-piece on the top of the handle, keeping the London needle in circuit with the York battery, and _vice versâ_. As soon as London uses his handle, it presses the spring-plate, and puts his needle out of the York circuit, the current he sets up sending York needle to the right or left, as the case maybe. The second wire connecting the left York plate with the right London plate is, it will be seen, not carried along like the first wire. Use is made in this case of the conducting power of the earth itself, plates from the wires being buried many feet below the surface at London and York. When London wishes to speak to York, he first signifies his intention of so doing by ringing York’s alarum. This he effects by sending a current through an electro-magnet placed above York’s instrument. The armature is attracted, and frees the detent of the alarum, setting it ringing until York signals ready. London then stops the bell, and commences his message. By following the direction of the current, when the handle is turned to the left, as in fig. 4 [within fig. 253], it will be readily seen how this is effected: commencing with London’s copper, LC, it passes up before and down behind London’s needle, flowing along the wire between the two cities to York’s needle, up before and down behind which it travels, sending it also to the left. It then passes to York’s right plate, through the connector to the left plate, and so on to earth at York, coming to the surface again at London, passing through London’s right plate and through the lower part of the handle to the zinc of the battery. The reverse current may be easily followed. Any number of instruments with similar needles may be interposed along the course of the wire. When the operator wishes to speak to any particular one, he rings all the bells for attention, and then signals Derby or Nottingham, as the case may be. They all then throw their instruments out of current except the one required. The mode by which the needle movements are converted into language is simple. A is signalled by causing the needle to vibrate once to the right, B once right and once left, C once right and twice left; and so on, as arranged.

The following is the alphabet (with numbers) once in use on the South-Eastern Railway for the double-needle instrument. The table is taken from Mr. Walker’s translation of De la Rive’s work on Electricity and Magnetism.

A is signified by two movements of left needle to left.
B ” by three ” ” ”
C (and fig. 1) by two ” ” right first, then left.
D (and fig. 2) by two ” ” left first, then right.
E (and fig. 3) by one ” ” to the right.
F by two ” ” ”
G by three ” ” ”
H (and fig. 4) by one ” right needle to the left.
I by two ” ” ”
J (same as G).
K by three ” ” ”
L (and fig. 5) by two ” ” right and left.
M (and fig. 6) by two ” ” left and right.
N (and fig. 7) by one ” ” to the right.
O by two ” ” ”
P by three ” ” ”
Q (same as K).
R (and fig. 8) by one parallel movement of lower points, both needles
to the left.
S by two ” ” ”
T by three ” ” ”
U (and fig. 9) by two ” ” first right, then left.
V (and fig. 0) by two ” ” first left, then right.
W by one movement of both needles (lower points) to right.
X by two ” ” ” ”
Y by three ” ” ” ”
Z (same as S) or specially.

The Morse system of telegraphy was first brought out in 1844, and was worked by means of a Voltaic battery, an electro-magnet being used at the receiving station. This magnet attracted an “armature,” and by it dots or lines are marked on a moving paper band by a point at the other end of the wire, on the register in which the paper is carried by rollers which move out by clockwork. The lever being “tapped” down in fast or slow pressures will give a corresponding series of dots or lines (according as the pressure is long or short) upon the moving strip of paper at the receiving station. Three taps will give C, one tap and a pause will make A. The dots are “taps” on the key, the lines brief “rests” on it, as will be seen from the alphabet below, which is given as a specimen.

MORSE ALPHABET.

A .-
B -...
C .. .
D -..
E .
F .-.
G --.
H ....
I ..
J -.-.
K -.-
L -
M --
N -.
O . .
P .....
Q ..-.
R . ..
S ...
T -
U ..-
V ...-
W .--
X .-..
Y .. ..
Z ... .

NUMBERS.

1 .--.
2 ..-..
3 ...-.
4 ....-
5 ---
6 ......
7 --..
8 -....
9 -..-
0 ___

The various stops are also indicated in the same manner by combinations of dots and lines.

The Atlantic telegraph cables and similar enclosed wires between other countries are too well known to need detailed description. There is a great variety of telegraphic instruments. The dial, and other arrangements, are very common, and the Wheatstone Key instrument is supplied to private firms as being the most handy. It requires but a very short apprenticeship, and any person who is handy can easily learn to work it in a few minutes. The apparatus consists of a dial upon which the letters of the alphabet are printed, each letter being supplied with a key or stop. A pointer is placed in the centre, as in the wheel barometer, and there is a handle beneath. In front, upon a sloping board, is another dial plate and pointer; thus we have the receiver and transmitter before us in a very small space.

When it is necessary to work the instrument a bell is rung by turning the handle rapidly. To speak by the instrument it is necessary to keep turning the handle with the right hand while the fingers of the left are employed in pressing down in as rapid succession as practice will permit the keys corresponding to the letters on the dial while the handle is kept turning. When a word is completed the operator must stop at the + at the top, and then begin again, stopping after each word. When all is said, a couple of rapid turns of the dial will signify that you have ended.

There are many other systems of telegraph, but all are dependent upon the same principles. The accompanying illustrations (figs. 254, 255) show a dial telegraph of a simple kind, which almost explains itself.

The first figure is the receiver, on which is a pointer fixed to a dial-plate having the letters of the alphabet inscribed around it. When the manipulator is being worked the dart points to the letters in succession of the words used, and they are separately spelt. The manipulator (fig. 255), by closing and opening the circuit, works the needle.

In the manipulator we have a wheel with an index point fixed above it. In this wheel are thirteen teeth, with the openings between them filled with ivory. The axis of the wheel is in contact with the wire from the positive pole, _p_, and a spring attached to the wire or by the binding-screw, _t_, presses against the circumference of the wheel, and completes the circuit. When the wheel is placed so that the arrow point is above the +, the needle of the receiver is also at +. By turning the wheel to bring the needle to A, the spring on the circumference is passed from an ivory “tooth” to a “metal” one; the circuit is closed, the point of the receiver also turns to A, and so on through the word by successive closing and breaking of the circuit.

As there are a great many other applications of electricity of which we have to treat,—the Electric Light, and Mr. Edison’s other inventions,—our space will not permit a much more detailed account of the telegraph, but there are some incidents connected with its progress which it would be as well to mention.

Alexander Bain, about 1840, attempted to produce a printing telegraph, and in 1846 he actually accomplished a registering apparatus, which was an application of the principles of Dyar and Davy. But although Bain’s system was good, Morse had the advantage of possession in the United States, where it was tried, and Bain went out of fashion. Bain’s system was, in fact, the present chemical “automatic” telegraph, which has been perfected for rapid transmission.

Bakewell’s instrument, which has been improved upon by later electricians, is termed the fac-simile telegraph. The message to be sent is written with a pen which has been dipped in varnish (for ink), and the characters are inscribed upon prepared tinfoil. The message is then put upon a cylinder covered with prepared paper, and has a pointer attached. There is a precisely similar cylinder at the receiving station. When the cylinders are simultaneously set going, the point at one will trace a spiral line as the first (transmitting) point passes round its cylinder. However, as the latter “stylus” meets the varnish letters a break occurs, and these spaces are exactly reproduced as blanks at the other end, and the form of the letters can be seen. Coselli, in his adaptation, caused dark letters to be registered on a white ground, and thus simplified matters. Since then we have had printing telegraphs, and dials, and writing machines, one of which will be described presently.

Submarine telegraphs were, it is said, first suggested by Salvá in 1797, and Wheatstone, in 1840, declared that it was quite possible to connect England and France by wire. Morse and Calt experimented with submarine cables in America, and Lieutenant Siemens first applied gutta-percha to the wires as an insulator in the Prussian line of telegraph across the Rhine. The English laid a wire between Dover and Calais, which was broken, but successfully relaid. And so on, till in 1857 the great project of the Atlantic cable was broached. We give illustrations of the cables; the circumstances connected with the laying of which, and the enthusiasm over the successful accomplishment of the task, must be in the memory of all. The readings of the messages were shown by delicate galvanometers, the beam of light being reflected from a mirror. This cable was lost, and in 1862 Mr. Field came over to urge the importance of the submarine cable between this country and America. The cable was shipped on the _Great Eastern_ in 1865, and was 2,186 miles long. It consisted of seven copper wires twisted, and covered with gutta-percha. The outside coating consists of ten iron wires surrounded by manilla yarn. But this cable broke, and a third was made and laid in 1866. The old cable was then recovered and spliced. There are some two hundred cables now in existence, the last being the Cape cable, laid when the Boer War was engaging our attention. The transmitting apparatus of Mr. Varley and Sir W. Thomson has greatly accelerated the rapidity of messages, and Thomson’s syphon recorder farther increased the speed.

The following description of a new system is from _Scribner’s Magazine_ for 1880:—

“NEW TELEGRAPHIC SYSTEM.

“A new system of sending and receiving electrical impulses over an insulated wire has recently been brought into successful operation, that seems to promise not only a radical change in the present methods of telegraphing, but a material gain in the speed and cost of sending messages by wire. It is founded on a union of the so-called “automatic” and “chemical” systems of telegraphy. The first of these employs a strip of paper having, by some mechanical means, a series of small holes punched in it, the design being to pass the perforated strip under a needle, or stylus, in electrical connection with the line. This stylus, on passing over the paper, opens the circuit, but in passing one of the holes, drops through and closes it,—this alternate making and breaking of the circuit transmitting the message. The chemical telegraph records any electrical impulses sent over a line by staining a strip of prepared paper passing under it. This is founded on the fact that electricity has the power of decomposing certain chemicals, and if paper is soaked in these chemicals and submitted to the action of electricity, it will be discoloured wherever the current passes. While both of these systems have been used, neither has been able to compete with the more simple Morse key and sounder, and it has remained for the new system to bring them to a position where they may come into general use. The new system is a modification and combination of the automatic and chemical systems, the transmitting being performed by means of a perforated strip of paper, and the receiving of the message being recorded by the discolouration of chemically prepared paper. The process is entirely mechanical and chemical, the telegraph operator having no direct control over the message, either by sight, sound, or touch. The written message is sent to the operating-room, and given to the person using the perforating machine. This consists of a small key-board, with black and white keys, each marked with a letter or sign, and an ingenious system of levers, operated by the keys, for punching small holes in a ribbon of paper moving past the side of the machine. The machine stands upon a small table, and under it is a treadle for giving motion to the feeding apparatus for supplying the paper to the machine. The operator moves the treadle with his feet, and at the same time touches each key to spell out the message. In a very few seconds the message is imprinted on the ribbon in the form of a double row of small perforations, each group of two holes representing a dash, and each single hole a dot, as in the Morse alphabet. Each letter is separated from the next by a longer dash, and each word by a still longer dash, and each sentence by a dash of indefinite length. This spacing of the letters is performed automatically, the spacing of words and sentences is performed by the operator. The perforated slip containing the message is then sent to the transmitting machine. This consists essentially of a metallic wheel, divided into two sections by means of a thin insulation of hard rubber. One section of the wheel is connected with the positive pole of the battery, and the other section with the negative pole. A pair of fine metallic brushes, both of which are connected directly with the line, are suspended above the wheel, and are arranged so as to press lightly upon the latter, when desired. When resting on the wheel the circuit is closed, and when raised above it the circuit is broken. The perforated strip is, by a simple piece of mechanism, made to pass over the face of this wheel and under the brushes. While the paper is passing, both brushes are raised from the wheel, and slide over the paper, and the circuit is broken. On passing a hole, one of the brushes drops through and closes the circuit for an instant. On passing two or more holes, arranged in a series close together, the brush closes the circuit for a shorter or longer time, according to the number of holes, and as the perforations on the paper are arranged in two rows, alternating from one to the other, the brushes are used alternately, and the polarity of the current is continually changed with every impulse sent over the line. No special skill is required in sending a message, as the operator has only to put the perforated strip in the machine and turn a hand-crank, to cause it to pass rapidly under the brushes, and with a little practice, a young girl can send messages at the rate of one thousand words a minute, with absolute precision. The receiving apparatus consists essentially of a simple piece of mechanism for causing a strip of chemically prepared paper to pass rapidly under two small needles that are connected with the line. As the paper passes the needles, the electricity sent over the line from the transmitting machine seeks the earth through the wet paper and the machine, and in passing discolours the paper, each stain representing a dot or dash, and the message is printed on the paper in a double row of marks at the same speed with which it was dispatched. In practice, a Morse key and sounder is placed at each end of the line, and on sending a message the transmitting operator calls the receiving station, and when the operator at the distant end replies, both turn the cranks in their machine swiftly, and the message is sent and received at an average speed of one thousand words a minute. The message received is given to a person using a type-writer, and at once translated into print and sent out by the messenger boy. It is found in practice that two operators, one at each end of a single wire of indefinite length, can keep fifteen operators fully employed in preparing the messages, and fifteen girls busy in translating and printing the messages for delivery. The system is of American origin.”

Of the hundred and one uses to which electric wires are now appropriated—of the alarms, fire-calls, clocks, etc.—we need not speak. We must pass on to the Writing Machine (fig. 258) before we make mention of Mr. Edison’s inventions.

The Writing Machine is as remarkable for the simplicity of its mechanism as for the facility and ease with which it can be used. It was invented by Remington, the American, whose name is so universally known in connection with a repeating rifle. He makes these writing machines in his own factory, where he associates them with rifles and sewing machines—implements for war and peace.

The appearance of the Writing Machine may be easily perceived from the illustration (fig. 258), which is drawn to scale one-fourth of the actual size. It comprises a key-board, upon which there are forty-four keys or stops, including numbers from 2 to 9, the _i_ and _o_ of the alphabet serving for numbers 1 and 0, and all the letters of the alphabet arranged in the manner most convenient for manipulation. There are also the various accents and stops, with note of interrogation, etc. The flat ruler at the base of the key-board is struck when it is necessary to separate one word from another.

In the interior of the apparatus every letter is attached to a small hammer, and corresponds to the pressure bestowed upon the notes, which are disposed in a circle. If A, for example, be touched upon the key-board, the hammer will bring A to the centre of the circle, and so every letter of the word will be, by such action, brought to the centre of the circle in succession. The paper upon which the letter is printed is wound upon a cylinder mounted upon a slide, as seen in the upper portion of the illustration.

When the letter is pressed down on the key-board the corresponding hammer strikes against the cylinder, between which and the hammer is a ribbon prepared with a special ink. The letter being in relief like ordinary type is impressed upon the paper. The slide upon which the paper is mounted is so arranged as to move from right to left exactly a letter-breadth after each impression. Thus as every hammer strikes at the same spot a regular succession of letters are printed off, the paper moving with regularity. When the line is filled—that is, when the paper has moved across the cylinder—a bell rings, and a handle is moved by the operator who is thus warned. The lever moved brings the slide back again, and a new plain surface is ready to commence upon the cylinder moving upwards at the same time, and displaying the printed line.

In operating both hands may be employed, but between each word care should be taken to press down the flat board at the base of the key-board, which has the effect of leaving a space upon the paper. Immediately the sound of the warning bell is heard the lever at the right-hand side must be lowered. The word can be finished in the line following if it be not concluded, the hyphen button being pressed to indicate the continuation.

The paper used must not exceed the width of the cylinder, but it may be of any less width, and a post-card or any small sheet of paper may be substituted. If the width be thus limited the length may be indefinite, and a very long line of paper may be used if desirable. The cylinder being made of gutta-percha offers a soft surface to the impression of the hammer, and causes the letter to assume greater distinctness.

The inked ribbon which passes underneath the paper is so arranged that no two successive letters strike it on the same place. It moves from an ink reservoir on the right to another on the opposite side, and it can be made to return beneath the paper, thus keeping up the supply. The impression being made in copying ink, the message or letter when finished can easily be reproduced in an ordinary press. The characters are all “capitals.”

At first it may be found a slow means of writing, and the manipulator may imagine he can do better without it. But if the author be certain of what he intends to say, after a little practice at the instrument, and when he becomes accustomed to the positions of the various letters, etc., the rate at which words can be printed off will far exceed that at which even rapid writers can work. A young English lady after some days’ practice was able to write as many as ninety words a minute with this machine—a rate more than double the average writing rate of penmanship. When such a rate or an approximation to it can be attained, those who are quick in their ideas will find the machine a great saving of time, and for any one afflicted with “writer’s cramp” the gain must be enormous. We need not insist upon the advantages the adaptation of the apparatus would confer upon editors and readers of MSS. too often badly written, and to compositors the invention is a great boon.

Finally, the working of the machine could be entrusted to the blind, and by teaching them the form of letters which could be raised upon the key-board, those so sadly afflicted could write with facility. Some methods for teaching the blind to manipulate and to read from the impressions of the hammers on the paper have already been tried with success.

The Electric Pen, an invention of the fertile brain of Mr. Edison, is shown in fig. 259. The “writing” consists of a series of little holes close together, made by a fine steel point like a put-crayon. This point is thrust in and out with great rapidity, and passes quickly over the paper. If the characters cannot be formed so quickly as with an ordinary pen, the writing is very distinct.

The alternative movement is given to the pen by an electric motor at once simple and ingenious, which is placed on the top of the penholder. The general appearance of the apparatus will be understood from the cut on next page.

The point is the termination of a wire which traverses the penholder, and the upper extremity of which catches on the motor by an eccentric. This eccentric has three teeth or cogs, and it makes sixty revolutions a second, thus producing one hundred and eighty beats in that time. The axle carries a plate of soft iron, which acts like the armature of an electro-magnet, before which it turns with great rapidity, the current being interrupted twice in every revolution by the commutator. The current which moves this little apparatus is furnished by a pile of two elements in bichromate of potash, according to Mr. Edison’s arrangement, which is considered very successful. Carbon and zinc are employed, and when ready for action the battery assumes the appearance of the cells in the illustration. When the operator wishes to discontinue writing, he simply raises the stem which has the electrodes attached to it, and the elements are thus preserved for a future time.

Under these circumstances the battery could be made to last several days without any renewal of the liquid, and the plates will last for weeks. Thus a very simple arrangement is at our disposal. Let us see what use can be made of it.

When we use the electric pen we obtain a great number of small holes close to each other. Such hand-writing is not easy to decipher by mere inspection like ordinary writing. By holding it up to the light it is more easy to read, but in both instances reading is not easy, nor does it come by nature as Dogberry declares. But if we consider the paper as a “negative,” we may obtain a number of positive proofs or copies of the writing. To obtain these successfully we must use a press, as shown in the accompanying illustration (fig. 260).

The writing, or negative, is placed upon the cover to the left, where it is firmly fastened. Upon the body of the press a sheet of white paper is placed, and when the lid is shut down the negative comes in contact with the paper. By means of a roller, represented in the box, the writing is blackened,—the ink penetrates into all the holes which are upon the paper,—and after the manner of a stencil plate the impression will be found upon the paper when the cover is removed. The writing will have a curious effect, but practice will speedily remove all deficiencies. The same negative will serve for a great many impressions, quite a thousand having been taken from one. By people accustomed to such work as many as six proofs a minute may be obtained. Of course a little practice will be necessary in this, as in every other case, before a correct or rapid result can be obtained, but there is no difficulty in the practice.

There are two or three other applications of electricity which we must refer to; such as the electric stamp, of which we give an illustration, and a curious method of stopping a horse by electricity. The electric stamp might be very advantageously employed in our post offices to obliterate the “Queen’s Head.” The description, with illustration of this apparatus, is annexed. (_See_ fig. 261.)

At the lower end of the apparatus is a thin platinum wire, so arranged as to form either a design or an initial; by this the postage stamp can be defaced. The stamp being put in communication with the pile, the circuit is closed by the pressure of the finger, as shown in the illustration. The platinum grows heated and carbonises the paper, and thus proves itself an ineffaceable stamp.

This apparatus may easily be used, not only by the post office authorities, but by every one who is obliged to deface a certain number of stamps every day, and wishes to do so rapidly and without possibility of error.

An ingenious, if scarcely necessary arrangement for conquering restive horses, and frightening them into submission, is shown in the illustration (fig. 262). Many means have been tried to stop or conquer a restive horse, but the most efficacious has been designed by M. Defoy; and the director of the Paris General Omnibus Company has experimented successfully, as we are informed, with the arrangement we are about to describe. A small magneto-electric machine is contained in a box beside the driver, within easy and convenient reach of his hand. The reins contain a wire, one end of which terminates in the horse’s bit, and the other in the electro-magnetic apparatus. When the electro-magnet is put in action an electric current is generated, which gives the horse a shock in the mouth, and so astonishes him that he suddenly stops in his course. If the operator have the humanity and good sense to unite kindness to the abrupt application of the electricity,—which in our opinion should be only used as a last resource,—no doubt some excellent results may be obtained even with vicious animals.

M. Bella, the Director of the Omnibus Company, has reported that the apparatus was tried in his presence and found very successful, and quite easy of application; and that even the most unruly animals have been subjected by it. On one occasion a most restive animal was thus treated on the way to the forge. He had a tremendous objection to be shod, and made no secret of his dislike. But a gentle application of the electric current put quite an opposite complexion upon the matter, and after a few minutes the animal permitted himself to be patted and caressed, and even allowed the smith to feel his legs and inspect his feet without making any objection whatever. His shoes were taken off, and the horse was re-shod without any of the dangerous demonstrations hitherto indulged in by the animal.

We may quote another instance of the efficacy of this method, which is reported from Paris by M. Camille.

“Many experiments have been made upon horses which had been most difficult to shoe, and in each case we have succeeded when the electric apparatus has been put in requisition. One horse, in particular, nothing could subdue. He kicked and bit and jumped about in such a manner as to render all approach impossible. We had recourse at length to M. Defoy’s apparatus, and after the first application, and without any great difficulty, we were able to raise the animal’s feet; but after a second lesson we were permitted to shoe him without his offering the slightest resistance. He was completely subdued.”

M. Defoy recently made the experiment with a very dangerous animal, which he stopped instantaneously in full gallop (_see_ fig. 262). It may be remarked that the application of the current is not sufficiently strong to stop the horse too suddenly. It merely causes a very unpleasant sensation—he is not stupefied nor galvanized by the electricity. The narrator has felt the shock applied without inconvenience, and the conclusion arrived at is, that this method of employing electricity is far superior to the violent and inhuman treatment so often employed to break horses, which renders them subsequently sulky and vindictive.

M. Defoy has completed an electric bit and an _electric stick_ quite as ingenious as the electric rein. The _modus operandi_ is simple and effective, the wires being insulated by leather, and terminating at the extremities of the stick. The current is induced, as before, by a small magneto-electric machine.

FOOTNOTES:

[15] _Encly. Metrop._

[16] “Treatise on Electricity and Magnetism.”

[17] Sabine: “The Electric Telegraph.”