126 



MAGIC LANTERN WITH MANTLE GAS LAMP [CH. V 



FIG. 68. UPRIGHT GAS BURNER WITH WELSBACH MANTLE AND 

 CONCAVE REFLECTOR FOR THE MAGIC LANTERN. 



(From Max Kohl, A. G., Price List No. 50, Vol. I). 



The distance from the condenser giving the best light must be 

 determined by experiment, as with 

 other extended sources. But, in gen- 

 eral, it will be found to be at about 

 the principal focal distance from the 

 first element of the condenser, as 

 with the arc lamp, but closer for the 

 two-lens than for the three-lens con- 

 denser (55). 



205. Reflector. As with the pe- 

 troleum light, a concave reflector is 

 sometimes used behind the mantle to 

 reflect back to the mantle and thence 

 to the condenser the light which passes 

 backward from the mantle. This is 

 not always used, but it would increase 

 the light somewhat ( 210). 



206. Connecting the gas supply 

 with the lamp. Use for this a perfect 

 rubber tube or one of the flexible me- 

 tallic tubes (fig. 60), and secure the 



FIG. 69. INVERTED GAS BIR- 

 NER WITH WELSBACH MAN- 

 TLE FOR THE MAGIC 

 LANTERN. 



(From Schmidt und llamch'a Cata- 

 logue, A'o. IV, Projektions Apparte, 



