202 



PHO T0-M1CR0GRAPHY. 



[CH. VIII. 



be turned to a higher number than the actual thickness of the cover 

 calls for (see § 96). 



§ 344. Photographing Without an Ocular. —Proceed exactly as 

 described for the lower power, but if the objective is adjustable make 

 the proper adjustment for the increased tube-length. 



§ 345. Photographing with a Projection Ocular. — Proceed as de- 

 scribed in § 343, only in this case the objective is not to be adjusted 

 for the extra length of bellows. If it is corrected for the ordinary 

 ocular, the projection ocular then projects this correct image upon the 

 focusing screen. 



Fig. 158. Zeiss' Vertical Pholo-micro- 

 graphic Camera. A. Set screw holding the 

 rod (S) in any desired position. P, Q. Set 

 screws by which the bellows are held in place. 

 B. Stand with tripod base in which the sup- 

 porting rod (S) is held. This rod is now 

 graduated in centimeters and is a ready 

 means of determining the length of the cam- 

 era. M. Mirror of the microscope. L. The 

 sleeve serving to make a light tight connection 

 between the camera and microscope. O. The 

 lower end of the camera. A\ The upper end 

 of the camera where the focusing screen and 

 plate holder are situated. ( From Zeiss' Photo- 

 micrographic Catalog). 



§ 346. Determination of the Magnification of the Photo-Micro- 

 graph. — After a successful negative has been made, it is desirable and 

 important to know the magnification. This is easily determined by 

 removing the object and putting in its place a stage micrometer. If 

 now the distance between two or more of the lines of the micrometer 

 is obtained with dividers and the distance measured on one of the steel 

 rules the magnification is obtained by dividing the size of the image by 

 the known size of the object (§ 146). If now the length of the bel- 



