18,681. Siemens Bros. Dynamo Works, and Holmes, E. A. Aug. 19. Search-lights.-An arc lamp for use as a searchlight has a casing so constructed as to facilitate access to the mechanism arranged therein. Screws for holding together the parts of the casing and of the carbon-holders, and a knob for feeding by hand, are made self-retaining to prevent their loss. Means are provided for adjusting the mechanism for various electric pressures and for preventing short-circuiting. The casing is divided longitudinally into two parts a, a', Fig. 2, retained in place by end caps d, d<1>. The part a has its upper portion trough-shaped, to retain broken pieces of carbon. Each cap is held by two studs e, the inner ends of which are enlarged and threaded, as shown in Fig. 7, so that they can only be withdrawn from the cap by unscrewing. The caps are secured by the studs to a frame consisting of flanged end plates b<2> and a plate b<4>. The lower part of the casing has its edges turned inwards to engage a groove in the frame. The mechanism is contained principally within the caps. A series electro-magnet f has an armature f pivoted at f and carrying a lever k, one end of which engages the plate b<2>. The other end of the lever, when the electro-magnet is first excited, collides with the end of a feed-screw h for the negative carbon-holder, thereby striking the arc. A spring j opposes this motion of the feedscrew. The positive carbon-holder gears with a second screw parallel to the first, both screws being geared by toothed wheels to a ratchet-w heel l. This is engaged by a pawl l<1>, Fig. 5, on the armature g<1> of a shunt electro-magnet g, the circuit of which includes a make-and-break device consisting of a fixed contact g' and a spring arm g<3> actuated by the armature. The motion of the armature is limited by an adjustable stop screw and is controlled by a spring p. The pressure of the spring can be adjusted, to suit various electric pressures, by means of a lever p<6>, p<5> attached to the spring and connected by a pin-and-slot to a rod p<2>, which can be moved longitudinally through the core of the electro-magnet g by a screw sleeve p<1> having a square end. Surrounding the sleeve is a knob q provided with a collar inside the casing for retaining it in position and connected by a clutch to the ratchet-wheel. The pawl l<1> may be thrown out of action, when the carbons are to be fed by hand, by a roller l<2>, Fig. 5, on an arm l<3>. This arm is attached to a hub (not shown) which surrounds the shank of the knob q and carries a finger outside the casing. Each carbon-bolder is supported by a pair of arms c, forked at their lower ends, and held by screws on carriers c'. The heads of the screws enter shallow recesses in the arms when screwed home. The inner ends of the screws are provided with collars, which may be held by small setscrews. The carriers c<1> are faced with asbestos or other non-combustible insulating-material t. The screws and sleeve p<1> can all be operated by one key.