4i8 OPTICAL PROJECTION 



Five wicks have been quite discarded. Three -wick lamps with 

 the same improvements have in some cases touched 90-candle 

 power. 



FIG. 233. Four-wick Oil Lamp 



Incandescent Gas tamps. This well-known form of gas- 

 burner is now in common use as a radiant. The light is not very 

 good, only amounting to some 70-candle power, and the definition 

 (owing to the great size of the mantle) leaves a good deal to be 

 desired. At the same time this form of light is so convenient, 

 requiring nothing but a gas-tap and a length of rubber tubing, and 

 is so white and clean, that in small halls and class-rooms, where a 

 disc of 8 or 9 feet suffices, it is, and will be, deservedly popular. 



The complete fitting, including mantle and burner, with a con- 

 cave reflector, is now sold at prices varying from 7s. Qd. to 10s., 

 and can be had of all leading opticians. 



Incandescent Spirit Burner. This is a burner essentialty the 

 same as the above, but using methylated spirit instead of gas, 



