focussing of the lamp is most ingenious. The lamp is first of all raised to the level of the focus, by means of the mechanism VI (Fig. 213), which raises or lowers the platform P; then it is placed in the focus itself by turning the shaft B′; this shaft controls, through a clock-train and an endless screw, the tube of the platform P, to which is bolted an eccentric, which displaces the lamp in an horizontal direction. Fig. 214.-Section through the focal plane. The electric arc is found to be in focus when its images refracted by the prisms at 90° m and n (Fig. 214) coincide with the tracings on two ivory plates fixed to the socket close to the lighting handles V and B' (Fig. 215). The lighting is thus effected from the outside of the apparatus, with the greatest simplicity and precision, and without looking at the dazzling light. The dotted lines of Fig. 213 indicate the substitution of an oil-lamp for one of the electric lamps. The electric lamps, three in number (two of them being reserve lamps), are reversed Gramme arc lamps, so as to obtain a fixed luminous point. In the lamp adopted at the Razza ABROISE ET COVETTER Fig. 215. Section through the sliding rollers. lighthouse, and which is represented in Fig. 216, the upper carbon remains fixed. In this figure will be seen the last of the train of clockwork R and its brake S controlled by the shunt magnet O. This brake is only released when the lamp is brought into focus. The current arrives in the |