Mr. Bain has invented and patented another kind of electric clock, the clock being in Glasgow, and the pendulum in Edinburgh. By means of the electric telegraph along the railway, constructed by Mr. Bain, he intimated his wish that the pendulum at the other end of the line should be put in motion. The clock was placed in the station-house in Glasgow, the pendulum belonging to it in the station-house at Edinburgh, the two being forty-six miles apart. They were joined by means of the wire of the telegraph, in such a manner as that, by a current of electricity, the machinery of the clock in Glasgow was made to move correctly, according to the vibrations of the electrical pendulum in Edinburgh. Thus, in like manner, were England and Scotland united in one great chronometrical alliance, a single electrical pendulum of this description, placed in the Observatory at Greenwich, would give the astronomical time correctly throughout the country.
The electric telegraph may be said to have originated in a trivial incident. It occurred to professor Oersted, of Copenhagen, to try the effect of a galvanic current on the needle of the compass. He found it, on making the experiment, deflected, that is, turned aside from its usual bearing of due north and south. Professor Wheatstone applied this result very ingeniously. He arranged a series of needles, mounted like that of the compass, and found that he could turn any of these aside by galvanic currents, while the others remained at rest. It was evident, therefore, that if each needle were supposed to denote a letter, any letters might thus be indicated; and, consequently, if an arrangement of needles standing for so many letters, respectively, were placed at the distance of fifty or a hundred miles, and any of them were acted on by means of wires traversing the distance, a message could be despatched at one end of the line, and read off at the other from the deflected needles, by any person duly acquainted with the arrangement. A similar set of needles at the opposite end, would enable him, as certainly, to transmit a reply.
The engraving represents the front of the telegraph, exhibiting the index, as it is denominated. The wires, which are suspended through the length of the line, are attached at either end to the telegraphic instruments, a branch wire being fastened to a large metallic surface, imbedded in the earth for completing the electric current. When at rest, the handles are down, and the pointers remain in their vertical position. The signals are given by two magnetic needles, or pointers, each suspended vertically on an axis passing through the dial, and, behind, another pointer is fixed on each corresponding axis. A portion of the conducting wire, many yards in length, is coiled round the galvanometer frame, in which the magnet moves, so as to subject the magnet to the multiplied deflecting force of the electric current.
The battery is the motive power of the machine, occupying the same relative position to it, as the boiler does to the locomotive; for, though it does not produce any immediate result on the works, yet the part it performs in the undertaking is essential. While travelling, Mr. Cooke found great inconvenience to result from the spilling of the acid solution used in Smee’s batteries; and, from this, he was led to consider if the substitution of fine white Shanklin sand, saturated with the diluted acid, would not avoid this difficulty. Experiments having confirmed the truth of his conjecture, the change was permanently arranged, and it was subsequently found so advantageous, that the same method was tried in the permanent batteries, and, in like manner, the result has proved satisfactory. At present, the generator resembles, in its principal features, the one known as Wollaston’s trough; and it is so arranged, that the series of plates of copper and amalgamated zinc, arranged for the evolution of the electric fluid, admit of being placed in a corresponding series of cells, filled with well-washed and dry sand. The United Service Gazette states, that all that is necessary in order to use the instrument is, slightly to moisten the sand with diluted sulphuric acid.
The conducting wires are, at their ends, of less diameter, and are so arranged as to form the coiled magnets. Those in the diagram are seen in connexion with the works; the electric current, taking the course indicated by the arrows, occasions the deflection of the needle.
The following engraving represents the interior of the machine, and shows the means by which the magnet is connected with the electric current. The parts lettered a are the key-shafts, which, on being turned to the right or left by a handle, pushes one of the springs, c, from its point of contact, d, and, by changing the course of the electric current, produces a corresponding change in the position of the needle.
In making a communication to the person stationed at the point where he wishes the information to be received, the operator, by turning the handle to the right or left, breaks the electric current; then, pressing the wire against pins connected with the battery-poles, the coils of wire receive their full deflective force, and attract the magnetic needles to either side, according to the course of the current. Thus, if the stream of electricity passes into the coil on the right, the upper part of the needle will be attracted towards it; if the stream passes into the coil on the left, then the needle will, in like manner, be attracted to it; thus, giving the whole motion necessary to the pointers. The time which elapses between the moving of the handles and the effect on the pointers, is imperceptible, though we must believe that it really follows it. The dial is divided into five circles, each containing a number of letters, or signs. The left-hand needle moving to the left twice, gives a; three times, b; once to the right and once to the left, c; once to the left and once to the right, d; once to the right, e; twice, f; three times, g. The order is then taken up by the right-hand needle moving once to the left for h; twice for i; three times for k; once to the right and once to the left for l; once to the left, and once to the right, for m; once to the right for n; twice for o; and three times for p. The remaining signs are made by two needles working conjointly, so that the simultaneous movement of the two, once to the left, indicates r; twice for s; three times for t; once to the right, and once to the left, for u; once to the right for w; twice for x; and three times for y. At the end of every word given, the left-hand needle, moving once to the right, to the cross, indicates that the word is completed. If the receiver understands the word, he signifies it by moving the same pointer twice to the left, and twice to the right, which means yes; if the communication is not understood, then the needle points twice to the right, and twice to the left, which indicates no. The original word is then repeated; if figures are wanted, the motions for each letter are doubled. Previously to giving a signal, the attention of the operator is called by the ringing of a bell, which is accomplished by an apparatus as simple as it is ingenious.[J]