Figure 79 represents that portion of the instrument which belongs to the _transmitting_ station, of which, K, is a circular disc, with the alphabet and numerals, marked in two concentric circles upon it: _a_ are handles projecting from its rim, one to every letter, by means of which, the disc is turned upon its axis, and brought to that position, _b_, required for signalizing a letter. O is a side view of the disc, K: _t_ is the rim of the disc, with its holders: _h_ is a portion of the axis of the disc, shown as broken off: _c_ represents a silver band surrounding a pulley, or hub, upon the axis, and directly behind the disc. Upon the hub are metallic ribs, _b_, parallel with its axis, corresponding in number to the letters on the dial. Each rib forms a metallic contact with the silver band, _c_, and are separated from each other by pieces of ivory, fastened to the hub. Both the ribs and ivory pieces are made perfectly smooth and even upon their surface: _e_ is a metallic spring with a portion of it pressing against that portion of the hub between the silver band, _c_, and the disc, _t_, in such a manner that when the disc is turned, the metallic ribs and ivory pieces shall alternately come in contact with it. To this spring is soldered a wire connected with one pole of the battery, _g_, and from the other pole proceeds the wire, _n_: _d_ is another metallic spring, similar to _e_, but pressing _only_ upon the silver band, with which it is always in contact, and to which a wire, _p_, is soldered. Whenever the spring, _e_, is in contact with any of the metallic ribs, there is a continuous connection from _n_ to _p_, viz. from _p_, to the spring in contact with the silver band, _c_, thence to the rib with which the spring, _e_, is in contact; then to the spring, _e_, then to the battery, _g_, and then to the wire, _n_. If, however, the disc, O, should be turned, so that the spring, _e_, is in contact with the ivory, then the circuit is broken at that point, and in this manner the circuit is alternately broken and closed as the wheel, O, is turned from one letter to another by means of the handles at _t_. [Illustration: FIG. 79.] [Illustration: FIG. 80.]