THE ELECTRIC TELEGRAPH.

SKETCH OF THE HISTORY AND PROGRESS OF THE ELECTRIC TELEGRAPH, WITH DESCRIPTIONS OF SOME OF THE APPARATUS.

I. EARLY OBSERVATIONS OF ELECTRICAL PHENOMENA.

1. THE history of the electric telegraph includes three distinct periods. The first of these embraces the earliest observations of electrical phenomena, their classification, and the inquiry into their physical causes. The second begins with the first suggestion of the application of electricity to the transmission of intelligence, and includes the experiments with frictional electricity. The third period dates from the discovery of galvanic electricity to the present time.

2. The phenomenon of electrical attraction produced by friction of bodies was, in some instances, known to the ancients. It was first noticed about six hundred years before the Christian era by Thales of Miletus, the founder of Ionic philosophy. He observed that when amber was subjected to friction it acquired the power of attracting light substances, such as bits of feathers; and on this account was led to attribute to it a species of vitality. The next mention we find is that of Theophrastus, who, three hundred

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years later, observed that a hard stone (supposed to be tourmaline), when rubbed, attracted straws and little pieces of sticks in its vicinity. Pliny (70 A.D.), as well as other naturalists, both Greek and Roman, remarked, at different dates, the same phenomenon, which they regarded, in the spirit of the times, with superstitious reverence.

The ancient philosophers appear to have been but little inclined to institute researches into the laws governing the natural phenomena they observed, partly because their studies were confined to observations made at long intervals and unassisted by experimental investigations, partly perhaps because the conservative spirit of the times discouraged such inquiries, by preferring fantastical theories combined always with superstition.

3. No systematic inquiry into the subject was undertaken until Dr. Gilbert, towards the close of the sixteenth century, at the expense of much pains, arranged and published in his celebrated work, "De Magnete," a list of all those bodies in which he had observed the same property.

Towards the middle of the seventeenth century Dr. Wall discovered the electric spark on rubbing a cylinder of amber with a piece of flannel. On approaching the cylinder with his finger he obtained, for the first time, the spark, and noticed the noise which always accompanies it.

Boyle-who observed that warmth increased the electrical effects and Otto Guericke, the inventor of the electrical machine, added to the little stock of electrical knowledge then in hand.

4. The first discovery which we have on record of the power of transmitting the electric fluid to a distance through an insulated wire is that of Stephen Grey, pensioner of the Charter House. Grey, having succeeded in electrifying a glass tube open at both ends, was desirous of finding out whether he could obtain the same result if he stopped up the ends with corks. This shows how at random the experiments were conducted at that date, and how little system

had been introduced into these inquiries. But Grey's experiment succeeded, and he was surprised to find the corks also highly electrified. On presenting the corked ends of the tube to a feather, he found that the feather was first attracted and then repelled. This led him to infer that the electricity which the tube had acquired by friction passed spontaneously to the corks. From the communication of electricity from tubes to corks Grey was led to transmit it through strings and wires; and in 1727 we find him employing a wire 700 feet long, suspended in the air by silk threads, to one end of which he brought his excited glass tube, whilst another person at the other end observed the electrification.

To Grey and Wheeler we owe the discovery that different materials possess different conducting powers. These physicists at first imagined that all materials would be equally capable of transmitting the electric impulse. In one of their experiments they employed a line formed of a hempen cord supported in the air by means of very fine silk fibre, believing that the loss of electricity at the points of support would be in proportion to the smallness of the diameter of the fibre, and that the greater part of the fluid would pass to the further end of the line. One end of the line supported. an electrometer formed of a small ivory ball and piece of feather; the other end was brought into contact with an excited glass tube. When Grey rubbed the tube Wheeler observed the bit of feather attracted towards the ivory ball. Experimenting in this way on one occasion, one of the supports of the line became injured, and, not having any more silk at hand, a piece of metallic wire was employed to replace it, from which moment no more electricity could be made to reach the further end; and Grey discovered that the conduction of electricity was not only dependent upon the thickness, but also upon the material of the body interposed.

5. After Grey the subject was taken up by Desaguilliers,

who instituted inquiries into the different conductibilities of bodies. The discoveries of Grey had caused the bodies operated on to be assorted into two classes, which Desaguilliers proposed to distinguish by the names of "electrics," or non-conductors, and "non-electrics," or conductors.

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6. On making experiments on the attraction of any light substance by an electrified body, it had been observed by Grey that the former was repelled from the moment that it was itself electrified by contact. It was further remarked that when the electrified body was a rod of glass, the light body would be strongly attracted by a stick of resin also electrified by friction. It is not a settled question whether it was Symner or Dufay, who, in 1733, first concluded, from the combination of these facts, the existence of two electricities. It was supposed that all bodies in their natural state contained an equal amount of each of these electricities in equilibrium, but that from the moment this equilibrium was upset, and until it was re-established, the elements would divide themselves between the rubber and the rubbed body-those identical with the electricity of a glass rod showing themselves in some bodies, and, in others, those of the same nature as the electricity of a piece of resin. This occasioned the former to be called vitreous electricity, and the latter resinous electricity.

7. Benjamin Franklin believed, however, in the existence of only a single fluid, and explained the phenomena by supposing that on exciting any substance till the equilibrium of the electricity was destroyed, an excess of it would be deposited on one side, and a deficiency, necessarily to the same amount, would occur on the other. Hence he gave the name of positive electricity to that which Dufay had called vitreous, and negative to that called resinous.

Dufay, without the remotest idea of the transmission of signals for practical purposes, and with the pure curiosity of

* Phil. Trans., vol. lxi., part i., p. 340.