CH. /'///] 



PHOTO-MICROGRAPHY 



239 



Such a microscope has the following general characters: The stage is 

 movable up and down with rack and pinion, it is rotary and more or less 

 mechanical by means of centering screws. With some at least the stage may 

 be removed entirely. No substage condenser is present, and a mirror is only 

 necessary for occasional transparent objects. A revolving nose-piece is not so 

 good as an objective changer. See Fig. 176. 



A 



FIG. 185 FIG. 1 86 



FIG. 185. Leitz' Vertical Illuminator. (From Leitz' Catalog.) 

 FIG. 186. Zeiss" Vertical Illuminator. (From Zeiss' Catalog.) 



\ 318. Illumination of Opaque Objects. (A) for 25 to 100 diameters. 

 The directions of Mr. Walmsley are excellent (Trans. Amer. Micr. Soc., 1898, 

 p. 191). "Altogether the best light for the purpose is diffused daylight. 

 Proper lighting is more easily obtained with a vertical camera. An even illum- 

 ination avoiding deep shadows is preferable in most cases and is more easily 

 attained with the object in a horizontal position. For many objects it is better 

 not to use a bull's eye or any form of condenser but for others the condenser 

 ma}- be needed, but when the condenser is used one must avoid too much glare. 

 The now little used parabolic reflector and Lieberkuhn serve well in many 

 cases, but he adds " the majority yield better results under the most simple 

 forms of illuminanion," /. e. , with the diffused light from the window. This 

 has been the experience of the writer also. 



In case diffused daylight is employed the camera should be near a good 

 sized window, and the object should be somewhat below the window ledge so 

 that the illumination is partly from above and from the side. (This is easily 

 attained with the small table and vertical camera shown in Figs. 165, 170, 171). 

 The vertical illuminator is advantageous for these powers also. See (B. ). 



(B) For 100 to 500 diameters, For the magnification above 50 it is 



