40 PHOTO-MICROGRAPHY 



would be known without measuring each 

 time. 



The focussing cloth may be used in the 

 usual way for low powers, but is almost out 

 of the question for high powers. With very 

 high powers the best way is to have a special 

 perfectly dark room for the camera. 



The Developer, Plates, &c. 



A convenient developer is that originally 

 issued as the Ilford Universal Developer, but 

 somewhat modified for ease of mixing. 



Very weak images to low magnifications can 

 advantageously be produced on process plates, 

 as these give great contrast. 



The higher magnifications must be done on 

 quick plates. 



The exposures vary from two seconds to 

 about two hours, or even longer. These long 

 exposures of the higher powers are very difficult 

 to keep free from vibration. The slightest 

 shake, as a matter of course, spoils the 

 negative. A good condenser will materially 

 shorten the exposure. 



