ELEMENTARY PHOTO-MICROGRAPHY. 15 



eyepiece in position remove the eyepiece, and imme- 

 diately a bright central spot of light will appear on 

 the paper. If the paper be now moved to or from 

 the end of the microscope, the bright spot of light 

 will gradually expand into a bright ring of light, and 

 then resolve itself into a point again. The whole 

 surface of the illuminated disc is, of course, much 

 more brilliant without the eyepiece, reducing expo- 

 sure considerably, yet the defect in uniformity of 

 illumination would spoil the negative. On replac- 

 ing the eyepiece the bright spot of light vanishes, 

 and the whole disc is equally lighted, though not so 

 brightly as before. 



First attempts should be made with well-defined 

 objects possessing contrast, such as the section of a 

 stem, rather than with those that are very trans- 

 parent all over. 



