28 ELEMENTARY PHOTO-MICROGRAPHY. 



and can be fed through a tube. If care be taken 

 to get uniform illumination by means of ground- 

 glass, then much time is saved by this light, which 

 is rich in actinic rays, but the beginner is not ad- 

 vised to try it until he has a good knowledge of all 

 the points to be observed in the taking of a perfect 

 negative. When using very oblique illumination 

 an exposure of two minutes with magnesium will be 

 found equal to sixty minutes with paraffin lamp. 



