108 



PHOTOGRAPHING BACTERIA. 



heavy block of wood B ; this can be pushed back upon the baseboard which 

 supports it, so as to allow the operator to place his eye at the eyepiece of the 

 microscope. When it is brought forward an aperture of the proper size ad- 

 mits the outer extremity of the eyepiece and shuts off all light except that, 

 coming through the objective. C is the microscope, and D the Abbe con- 

 denser, supported upon the substage. E is a thick asbestos screen for pro- 

 tecting the microscope from the heat given off by the battery of gas burners 

 F. This asbestos screen has an aperture of proper dimensions to admit the 

 light to the condenser D. The gas burners are arranged in a series, with 

 the flat portion of the flame facing the aperture in the asbestos screen E. 

 The concave metallic mirror G is properly placed to reflect the light in the 

 desired direction. I have not found any advantage in the use of a condens- 

 ing lens other than the Abbe condenser upon the substage of the microscope. 

 The focussing is accomplished by means of the rod I, which carries at one 

 extremity a grooved wheel, H, which is connected with the fine adjustment 

 screw of the microscope by means of a cord. 



' ' The focussing wheel J may be slipped along the rod I to any desired 

 position, and is retained in place by a set screw. The rod I is supported 



FIG. 74. 



above the camera by arms depending from the ceiling, or by upright arms 

 attached to the baseboard. 



" I have lost many plates from a derangement of the focal adjustment 

 resulting from vibrations caused by the passing of loaded wagons in the 

 street adjoining the laboratory in which I work. This has been overcome 

 to a great degree by placing soft rubber cushions under the whole appa- 

 ratus." 1 



Students who desire to perfect themselves in the art of making 

 photomicrographs are advised to first make themselves familiar with 

 the technique of photography with a landscape or portrait camera, 

 and not to undertake the more difficult task of photographing bac- 

 teria until they know how to make a good negative and to judge 

 whether an exposure has been too long or too short, etc. 



1 From Johns Hopkins University Circulars, vol. ix., No. 81, p. 72. 



