ELEMENTARY PHOTO-MICROGRAPHY. 43 



An iris diaphragm and disc plate ; 

 A mechanical stage ; and 

 A coarse and fine adjustment. 



The advantage of a short tube is seen in the 

 much larger field when using low powers. If the 

 microscope have a polariscope attachment, all the 

 better, but this is not essential. 



It should have two eyepieces, A and C, and a 

 battery of good objectives, say, to begin with, 

 3in., 2in., iin., Jin., to which may be added after- 

 wards Jin. and ^in. oil immersion, as the reader 

 feels his way to use higher powers. All these should 

 be kept free from dust and carefully cleaned with 

 washleather before use. The washleather should 

 be kept in a stoppered jar and used only for this 

 special purpose. Cleanliness throughout is of the 

 highest importance. A mere dust over with a 

 pocket handkerchief is not sufficient. The mounted 

 object to be photographed should also be rubbed 

 back and front, for it is astonishing how readily 

 dust and hairs adhere, and it must be examined 

 with the focussing glass before one can be satisfied 

 that it is clean. Due attention must also be given 

 to the eyepiece, because any specks of dirt left 

 thereon will inevitably appear in the form of pin- 

 holes or patches on the negative. 



Caution when touching the oil lamp not to 

 grease the fingers is advisable. A short black velvet 



