[Illustration: FIG. 61.] _Mr. Elisha Gray’s System._--According to the system originally patented, each sender, represented fig. 61, consists of an electro-magnet M M resting below a small copper tablet B S, in such a way that its poles pass through this tablet and are on a level with its upper surface. A steel plate A S is fixed above these poles; its tension can be regulated by means of a screw S; and another screw _c_ is placed on the plate, and is in electric communication with a local battery R′ by means of a Morse key. Below the plate A S there is a contact _d_ connected with the line wire L; this contact is met by the plate at the moment of its attraction by the electro-magnet, and breaks the current of a line battery P, which acts on the receiver of the opposite station. Finally, the electric communication established between the local battery R′ and the electro-magnet, as may be seen in the figure, produces vibrations in the steel plate A S at each lowering of the key, as in the case of ordinary vibrations--vibrations which, with a suitable tension of the plate and a given intensity of the battery R′, can produce a definite musical note. Moreover, since at each vibration the plate A S meets the contact, discharges of the line current take place through the line L, and react on the receiving instrument, causing it to reproduce exactly the same vibrations as those of the sending instrument. [Illustration: FIG. 62.] The receiving instrument represented fig. 62 exactly resembles the one we have just described, except that there is no contact _d_ below the vibrating plate A S, and the contact _c_, instead of communicating with the line wire, is in electric connection with a register E and a local battery P. It follows from this arrangement that when the plate A S vibrates under the influence of the broken currents passing through the electro-magnet M M, similar vibrations are sent through the register; but if the electro-magnetic organ of this register is properly regulated, these vibrations can only produce the effect of a continuous current, and hence the length of the traces left on the instrument will vary with the duration of the sounds produced. In this way the registration of the dashes and dots which constitute the signs of the Morse vocabulary will be effected.