CH. VIII'\ PHOTO-MICROCKArilY 221 



2 297. Size of Camera. The majority of photo -micrographs do not 

 exceed 8 centimeters in diameter and are made on plates Sxii, 10x13 or 13x18 

 centimeters (3'|x4 ' 4 in., 4x5 in., or 5x7 in.). Most of the vertical cameras 

 are for plates not exceeding 10x13 centimeters (4x5 in.) but Zeiss' new form 

 will take plates 21x21 centimeters (S'^xS 1 ^ in.). 



2 298. Work Room. It is almost self-evident that the camera must be in 

 some place free from vibration. A basement room where the camera table 

 may rest directly on the cement floor or on a pier is excellent. Such a place 

 is almost necessary for the best work with high powers. For those living in 

 cities, a time must also be chosen when there are no heavy vehicles moving in 

 the streets. For less difficult work an ordinary room in a quiet part of the 

 house or laboratory building will suffice. 



2 299. Arrangement and Position of the Camera and the Microscope. 

 For much photo-micrography a vertical camera and microscope are to be pre- 

 ferred (Fig. 170). Excellent arrangements were perfected long ago, especially 

 by the French. (See Moitessier.) 



Vertical photo-micrographic cameras are now commonly made, and by 

 some firms only vertical cameras are produced. They are exceedingly con- 

 venient, and do not require so great a disarrangement of the microscope to 

 make the picture as do the horizontal ones. The variation in size of the pic- 

 ture in this case is mostly obtained by the objective and the projection ocular 

 rather than by length of bellows (see below Fig. 170). It must not be forgot- 

 ten, however, that penetration varies inversely as the square of the power, and 

 only inversely as the numerical aperture ( $ 40) , consequently there is a real 

 advantage in using a low power of great aperture and a long bellows rather 

 than an objective of higher power with a short bellows. A horizontal camera 

 is more convenient for use with the electric light also (Fig. 180) . 



For convenience and rapidity of work a microscope with mechanical stage 

 is desirable. It is also an advantage to have a tube of large diameter so that 

 the field will not be too greatly restricted (Fig. 176). In some microscopes 

 the tube is removable almost to the nose-piece to avoid interfering with the 

 size of the image. The substage condenser should be movable on a rack and 

 pinion. The microscope should have a flexible pillar for work in a horizontal 

 position. While it is desirable in all cases to have the best and most conven- 

 ient apparatus that is made, it is not by any means necessary for the produc- 

 tion of excellent work. A simple stand with flexible pillar and good fine 

 adjustment will answer. 



\ 300. Objectives and Oculars for Photo-Micrography. The belief is 

 almost universal that the apochromatic objectives are most satisfactory for 

 photography. They are employed for this purpose with a special projection 

 ocular. Two low powers are used without any ocular (Fig. 183). Some of the 

 best work that has ever been done, however, was done with achromatic objec- 

 tives (work of Woodward and others). One need not desist from undertaking 

 photo-micrography if he has good achromatic objectives. From a somewhat 

 extended series of experiments with the objectives of many makers the good 



