ELEMENTARY PHOTO-MICROGRAPHY. 67 



The size of the image as well as its sharpness 

 may be varied by moving the transparency to or 

 from the condenser, or by altering the focus of 

 substage condenser or the objective. When satis- 

 factory definition is obtained, couple up the camera 

 and photograph. 



RECORD WORK AND CIRCULATING ALBUM FOR 



MICROSCOPICAL SOCIETIES. 

 It sometimes happens that an object is under 

 observation of which a record is desirable, and of 

 which it is not possible to obtain a slide prepared 

 and mounted for photography. When such an 

 occasion arises, as it often does in the study of 

 pond life, more particularly the very transparent 

 infusoria, a sketch can be drawn to scale with 

 sufficient exactness for purposes of identification by 

 using a micrometer ruled in squares in the eyepiece. 

 This consists of a thin glass disc mounted in a 

 brass ring, as sketch, fig. 23, on which a square 

 is drawn, having each side divided into ten parts, 

 thus giving a space ruled into 100 squares. Every 

 portion of an object under view, therefore, is seen 

 to lie in one or other of these divisions, as in 

 fig. 23. 



A similarly ruled square, but enlarged, say, ten 

 times that in the eyepiece, is made on paper, when 

 it is an easy matter to transfer the outline of any 

 object from one square to the other. 



