On handle, E, presses continuously the spring, H, Fig. 3, bringing the current coming from the selenium line. The cogged wheel in Fig. 5 has at a certain point of its circumference the sliding spring, O, Fig. 5, intended to slide as the wheel revolves over the different contacts of disk, A, Fig. 3. This cogged wheel, Fig. 5, is turned, as in the dial telegraphs, by a rod working in and out under the successive movements of the electro-magnet, H, and of the counter spring. By means of this rod (which must be of a non-metallic material, so as not to divert the motive current), and of an elbow lever, this alternating movement is transmitted to a catch, G, which works up and down between the cogs, and answers the same purpose as the ordinary clock anchor. [Illustration: FIG. 3] This cogged wheel is worked by clockwork inclosed between two disks, and would rotate continuously were it not for the catch, G, working in and out of the cogs. Through this catch, G, the wheel is dependent on the movement of electro-magnet. This cogged wheel is a double one, consisting of two wheels coupled together, exactly similar one with the other, and so fixed that the cogs of the one correspond with the void between the cogs of the others. As the catch, G, moves down it frees a cog in first wheel, and both wheels begin to turn, but the second wheel is immediately checked by catch, G, and the movement ceases. A catch again works the two wheels, turn half a cog, and so on. Each wheel contains as many cogs as there are contacts on transmitter disk, consequently as many as on circular disk, A, Fig. 3, and on brass disk within camera. [Illustration: FIG. 4] [Illustration: FIG. 5] Having now described the several parts of the apparatus, let us see how it works. All the contacts correspond one with the other, both on the side of selenium current and that of the motive current. Let us suppose that the slide of transmitter is on contact No. 10 for instance; the selenium current starting from No. 10 reaches contact 10 of rectangular transmitter, half the slide bearing on this point, as also on the parallel rail, communicates the current to said rail, thence to line, from the line to axis of cogged wheel, from axis to contact 10 of circular fixed disk, and thence to contact 10 of receiver. At each selenium contact of the rectangular disk there is a corresponding contact to the battery and electro-magnet. Now, on reaching contact 10 the intermission of the current has turned the wheel 10 cogs, and so brought the small contact, O, Fig. 5, on No. 10 of the fixed circular disk. As may be seen, the synchronism of the apparatus could not be obtained in a more simple and complete mode--the rectangular transmitter being placed vertically, and the slide being of a certain weight to its fall from the first point of contact sufficient to carry it rapidly over the whole length of this transmitter.