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.