ELEMENTARY PHOTO-MICROGRAPHY. 



A record of all exposures should be kept, enter- 

 ing the failures as well as the successes ; it should 

 note the plate used, the class of object photo- 

 graphed, with its characteristic quality, the ex- 

 posure, the distance of the plate from the object, 

 and the result with each power and with each 

 class of illumination. Supposing this to be done, 

 and one wishes to know what exposure to give to 

 a cheese mite, using the lin. objective and the 

 A eyepiece, reference to the register shows, say, 

 the following : 



EXPOSURE RECORD BOOK. 

 lin. Objective. Transmitted Light. 



None 



Cheese mite 



Slow 



Green 



Too little 



Under the head of Illumination, the following abbreviations may be 

 used : T, for transmitted light ; R, reflected light ; D, dark ground ; 

 O, oblique illumination ; P, polariscope. 



