84 HOW TO USE THE MICROSCOPE 



focussing screen of the camera. The mirror of the 

 microscope is not required, so it is turned aside ; 

 and it may be as well to state that the camera lens 

 is removed because the micro sco pe is itself al ens^ ' 



In my own work I invariably use an eye-piece 

 in the microscope ; by so doing I do not need a long 

 extension of the camera bellows ; the bellows ex- 

 tension needed is much greater when the eye-piece 

 is discarded. 



Perfect illumination of the object is of the highest 

 importance. Using a metal filament electric lamp 

 enclosed in a box whitened inside, with a 3 x 1-inch 

 aperture for escape of light, and diffusing the light 

 with a slip of ground glass, I have obtained good 

 results without any substage accessory when working 

 with very low powers. But when an ordinary oil 

 lamp is used, I have no hesitation in saying that, 

 with aU powers, some accessory is required. With 

 objectives 1 inch and lower, the light can be parallel- 

 ized with a bull's-eye condenser (p. 33), in which 

 event light, condenser, object, and microscope must 

 be in perfect line. It is not wise to use more rays 

 than are really required, and the diaphragm is 

 needed to cut off unnecessary ones. With objectives 

 higher than 1 inch a substage condenser is necessary 

 for critical illumination. 



To take a photograph, we first put the object in 

 position on the microscope stage and focus it roughly. 

 Then we connect microscope tube and camera, 

 seeing that they are in perfect line. Having arranged 

 the light, we focus the image projected on the 

 focussing screen of the camera. If the image is 

 not large enough to fill the screen, we extend the 



