CH. Ill] 



ARC LAMPS WITH SMALL CURRENTS 



are used (fig. 496), is to leave the wires as they are in thelamp.but 

 pull the separable plug apart and turn it half way round. This will 

 reverse the position of the connections so that the polarity will be 

 found correct on lighting the lamp again. 



When the correct polarity has been obtained at one particular 

 lamp socket it is well to make a straight line with a glass pencil, a 

 pen or a brush across the socket, and the two parts of the separable 

 plug, then the correct connections can be made with that socket at 

 any time without trouble. 



Arc Lamp 



KS 



FIG. 46. THE MAGIC LANTERN FOR USE ON THE HOUSE LIGHTING 



SYSTEM. 



SW Supply wires to the lamp socket (So). 



So, K The lamp socket with the key switch. 



S P Separable attachment plug. The cap has been removed to show 

 the metal prongs serving to make the contact. 



L W Wires connecting the cap of the separable plug with the knife switch. 

 (K S). As shown in fig. 45, 47, the knife switch is more frequently omitted. 



K S Double-pole knife switch for opening and closing the circuit. 



Rheostat For controlling the current. It is in one wire. 



Arc Lamp This is one of the small forms. 



5 5 Set screws for holding the carbons in place. 



h c Horizontal or upper carbon. 



v c Vertical or lower carbon. 



In In Insulation between the carbon holders and the rest of the lamp to 

 compel the current to follow the carbons, and not to short circuit. 



fs Feeding screws for moving the carbons. 



cl Clamp to fix the lamp at any desired position on the vertical rod. 



Condenser The two-lens condenser for illuminating the lantern slide. 



i 2 The two plano-convex lenses with their curved surfaces facing each 

 other. 



L S Lantern slide close to the condenser. 



Axis Axis The principal optic axis of the condenser and the objective. 



Objective The projection objective for giving the screen image. 



Image Screen The white screen on which the image is projected. 



