44 THE A B C OF PHOTO - MICROGRAPHY 



bly the most highly actinic of any artificial 

 light, but the smoke and dust accompanying 

 its combustion, together with the compara- 

 tively high cost of the material, preclude its 

 general use where much work has to be done. 

 Special means may be devised for disposing of 

 the fumes and dust, but, on the whole, burn- 

 ing magnesium as a radiant is not likely to be- 

 come very useful in continuous work. 



The lime light seems to be the most com- 

 mon form of radiant in England for photo- 

 micrography. This is doubtless due to greater 

 facilities for procuring the necessary oxygen 

 and hydrogen gases afforded in that country, 

 together with correspondingly lesser ones for 

 obtaining the electric current than prevail in 

 the United States. The light is highly actinic, 

 very intense, and capable of doing rapid and 

 excellent work, but its management is vastly 

 more complicated and troublesome than that 

 of the electric arc. It is, possibly, used to 

 some extent in this country, but I do not know 

 of any one so doing. 



In my estimation the most generally useful 

 radiant is acetylene, "a chunk of sunlight 

 brought down to the work table," as some 

 one has aptly remarked. Its brilliance, steadi- 

 ness, actinic qualities and cheapness all recom- 



