CH. Ill] MAGIC LANTERN WITH SMALL CURRENTS 



79 



FIG. 41. THE LILIPUT ARC LAMP OF LEITZ. 



This lamp was designed to use with the Edinger drawing apparatus and with 

 the condenser for dark ground illumination, etc. Both carbons are moved 

 equally by means of the rack and pinion movement. For direct current the 

 horizontal or positive carbon is larger than the vertical or negative carbon in 

 the proportion of 8 to 6. 



The condensing lens in the tube is mounted in a telescoping sleeve. When 

 the sleeve is in, the lens is at its principal focal distance from the crater, and 

 gives a parallel beam of light. When the sleeve is pulled out more or less the 

 condenser gives a converging beam of light. 



For use with the magic lantern the tube and special condenser are removed, 

 as shown in fig. 47. 



adapters for the small carbons. Such carbons require from three 

 to six amperes of current for the best effect (fig. 41-44). 



(2) A Nernst lamp with one or more filaments (fig. 54-55). 



(3) A Mazda lamp with concentrated filament (fig. 52). 



The arc lamp is permanent. One has simply to renew the 

 carbons when they are burned out. 



If alternating current is used, carbons 150 mm. (6 in.) long and 

 8 mm. ( 5/ i<5 in.) in diameter last about three hours. 



If direct current is used the upper carbon is 8 mm. ( 5 /ir, in.) 

 and the lower carbon 6 mm. (^4 in.) in diameter. Both are 150 

 rrm. (6 in.) long, and they last about three hours ( 753a). 



The Nernst and Mazda lamps are fragile and must be handled 

 carefully. They have a working life of 500 hours, more or less, 

 then a new lamp must be obtained. 



