THE RADIANT AND ILLUMINATION 45 



mend it to the photo-micrographer. In the 

 latter quality it rivals coal oil. A pound of 

 calcic carbide, costing 4 cents, furnishes me 

 with a full supply of light for a week's work. 

 Of course steady burning would require more 

 material, but for several hours' work per day 

 or night, with a burner consuming A of a 

 cubic foot of gas per hour, I find, as stated, 

 that one pound of carbide lasts a full week. 

 The light is extremely actinic (probably fully 

 equal to that of the lime light) , though its inten- 

 sity is much less, requiring considerably longer 

 exposures than the latter vastly shorter, how- 

 ever, than those necessary with a coal oil lamp. 

 I have used it almost exclusively in my work 

 for more than five years, and therefore am in a 

 position to speak conclusively as to its merits 

 and capabilities. 



The Welsbach incandescent gas light is 

 one of the very best sources of light for low 

 and medium powers, but not well suited to 

 high amplifications, and utterly useless in 

 " critical" illumination, as will be shown later 

 on. The light is brilliant, intense and much 

 more actinic than that of the best coal oil 

 flame. It is very easily manipulated and 

 almost universally available, as a supply of 

 gas may be obtained in all cities and towns 



