Page:Popular Science Monthly Volume 44.djvu/62

 of two light aluminum arms, making a right angle with each other. Each of these arms is attached to its operating drum by means of a cord passing around the drum, so that the rotation of this moves the arm to and fro in the direction of its length after the manner of the ordinary bow drill. The drums are given a tendency to rotate by a small electric motor located in the case of the receiver, and as this rotation is controlled by the polarized relays, which are in turn operated by the current impulses sent out by the transmitting pen, it will be seen that the movement of this latter determines that of the receiving pen, both in amount and direction, and that hence the two pens must move in exact accordance



with each other. The mechanism of the receiving instrument is at present a little intricate, and some of the operations to be performed, as the lifting the pen from the paper, shifting the paper, and reversing the motion of the operating drums, require in the present construction two additional line wires, but these, it is expected, can by contemplated improvements be dispensed with, leaving only two line wires for the performance of all the necessary operations. The system has so far been operated over a distance of only thirteen miles; but from the character of the currents used—distinct successive electric impulses—there would seem to be no reason why it should not be capable of operation over as long distances as the ordinary telegraphic instruments.