from a state of concealment to a state of exposure, or the reverse, by passing through a comparatively small angle, and by arranging the disk-lever _e_, as shown in the drawing, in such a manner that in bringing the disk from a state of concealment to a state of exposure, or the reverse, said lever _e_ shall swing to and beyond a horizontal position, the greatest uniformity of motion with the least possible loss of power are secured. Having thus described the construction of the visual signal G, it will be seen that when the electro-magnet M is charged it attracts the armature _m_ to itself, thus swinging the upper end of the lever L in the direction of the arrow _z_, and carrying the upper end of the lever _g_ forward, at the same time turning the same together with the lever _e_ on the axis _f_, and carrying the disk S down into the position indicated in dotted outline. Now connect one pole of the battery B with the rails _a_ and _c_, and the other pole with the rails _b_ and _d_ of the sections C and C' by means of the wires _k_ and _k'_, respectively. In like manner connect the ends of the coils of the magnet M, the one end with the rails _a_ and _c_ and the other end with the rails _b_ and _d_ of the same sections C and C' by the wires _l_ and _l'_, as shown in the drawing, and the apparatus is operative. The wires from the battery and the signal to the track are preferably insulated. Before describing the operation of the apparatus as a whole, it may be stated that the electric current will follow a naked metallic conductor if of sufficient surface, even when immersed in a river or in the mud at the bottom of a river, because the metal offers less resistance to its passage than either water or mud. Much more will it follow the rails of a railroad track when they are made a part of the circuit, since the rails present a large surface of good conducting material, which offers much less resistance to its passage than any surrounding mediums; and it is well known that when several courses are presented the electric current will follow that course which offers least resistance to its passage.