54 ELEMENTARY PHOTO-MICROGRAPHY. 



Oblique light, although very good for visual 

 inspection, is ill-adapted for photography, and 

 without great care will result in a blank negative, 

 even after long exposure. False images are also 

 created by oblique light, which introduces sources 

 of error only detected by an experienced micro- 

 scopist. 



The writer has never found the Lieberkuhn of 

 any advantage in illuminating opaque objects. A 

 reflector called a vertical illuminator may be tried 

 when the lens approaches so near to the object that 

 it is difficult to project a beam of light from the 

 side reflector. It is especially useful for photo- 

 graphing metals with high powers or objects 

 mounted dry on cover. 



