Page:Popular Science Monthly Volume 3.djvu/419

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405
ELECTRIC TELEGRAPHS.

To send a current to another station, the handle (H) is moved to one side, and the current sent will be positive or negative according to the side to which the handle is moved. The handle turns the cylindrical arbor (a b), which is divided electrically into two parts by an insulator in the middle of its length. Each of these parts has a pin projecting from it, one pin being above, and the other below. These are vertical when the handle is vertical, and are then doing no duty; but, when the handle is put to one side, the upper pin (which is attached to b) makes contact with one of the tall springs (t t'), at the same time pushing it away from the metallic rest (k), and thus putting it out of connection with the other tall spring; while the lower pin (which is attached to a) makes contact with one of two short springs (T T), only one of which is shown in the figure. There is permanent connection between a and the negative pole of the battery through the spring s, and between b and the positive pole through the spring s' . In the position represented in the figure, a serves to connect the negative pole of the battery with the earth, and b serves to connect the positive pole with the spring t', down which the current passes from the point of contact of the pin, and then through the coil to the line-wire at L. The needle of the sending station is thus deflected to the same side as that of the receiving station.

Fig. 4.
PSM V03 D419 Breguet indicator.jpg
Breguet's Indicator.

If the handle were moved to the other side, b would serve to connect the positive pole with the earth, and a would establish connection between the negative pole and the coil, which is itself connected with the line-wire.

Since the English telegraphs came into the hands of the post-office, the alphabet devised by Wheatstone and Cooke has been given up, and the Morse alphabet, which we give in a later section, adopted in its