66 THE A B C OF PHOTO - MICROGRAPHY 



Medium Powers by Transmitted Light. There 

 is but little material difference in the manipu- 

 lations between photo-micrography with low 

 or medium amplifications. Under one hun- 

 dred diameters which is generally termed low 

 power work a substage condenser may fre- 

 quently be dispensed with advantageously. 

 But in using medium powers one hundred to 

 five hundred diameters it should always be 

 employed, not only to shorten exposures, but 

 to insure the best rendition of the object. 

 With high powers its use is absolutely neces- 

 sary. It is also requisite to provide some 

 means for moving the fine adjustment screw 

 when the camera is extended so far that it 

 cannot be reached by the hand during exami- 

 nation of object upon the focusing screen. 

 This may be done by means of a rod and 

 pulley-wheel, as described on page 25 and 

 shown in Figures 4, 5 and 6. If this is not 

 available, a series of screw-eyes may be ar- 

 ranged on both sides of the camera platform, 

 through which a fine cord (as a fishing line) 

 can be strung, passing around a groove in the 

 periphery of the micrometer screw and kept 

 taut by means of a small weight attached to 

 each end hanging from rear of the camera 

 platform. A very slight pull upon this cord 



