AND SUPER MICROSCOPE 



little " depth of focus." The experienced landscape 

 photographer, did he wish all three objects to appear 

 equally sharp could easily attain his object. He 

 would perform the simple operation known as stop- 

 ping down his lens, that is to say he would gradually 

 close its diaphragm, while viewing the scene on the 

 ground glass. At a certain point everything would 

 be sharp, from foreground to distance. At the 

 smaller aperture of the lens, caused by closing the 

 diaphragm, the depth of focus would be consider- 

 ably increased, at the same time much less light 

 would be admitted to the camera. Looking upon 

 our object, under the microscope, as comparable 

 to a landscape, seen on the ground glass focussing 

 screen of a camera, it is obvious that, unless our 

 object has no thickness, and this is impossible, we 

 cannot highly magnify its upper and lower surfaces 

 at one and the same time. There are no adjustable 

 diaphragms in the objective so our only course is 

 to examine the two surfaces in turn or to resort to 

 a lower magnification. 



Apart from any other consideration, the super 

 microscope marks a big advance from the fact that 

 it possesses great " depth of focus." It is possible, 

 for example, with this remarkable instrument to 

 examine a moss as it grows, with a high magnifica- 

 tion and see not a portion of a leaf or a fragment 

 of the stalk, as with the ordinary microscope, but 

 the whole upstanding plant, in stereoscopic relief. 

 It shows us objects exactly as we should see them 

 were we endowed with super eyes, enormously en- 



241 Q 



