CH. VIII '] 



PHO TO-MICR OGRAPHY 



207 



ning down in the vertical position a pawl is held in place by a spring. This may 

 be released by a smaller wheel than that serving to move the pinion. This rack and 

 pinion are fine enough for focusing with the photographic objectives employed. 



Fig. 169. 



The camera bed is graduated in centimeters so that the exact extent of the 

 bellows can be determined by inspection. 



The support on which the specime?i rests is of heavy glass on vertical 

 rods about 10 centimers long. The background is placed on the table top about 10 

 cm. below. This arrangement of support and background serves to avoid the dense 

 shadows which make it difficult to determine exactly the limits of the specimen. 

 To make the apparatus steady the right hand end of the table is heavily weighted. 

 The tables have leveling screws in the legs. 



