48 



The Electron Microscope 



Fig. 15a 



cal aberration would have very poor resolution. The effect 

 corresponding to inelastic collisions is absent in ordinary micro- 

 scopy, as light in general does not change its wavelength in the 

 object. An exception is fluorescence microscopy. In this case, 

 it would be possible to imitate the working of the electron micro- 

 scope by reversing the usual process. Instead of observing the 

 visible fluorescence through chromatically corrected objectives, 

 one could use lenses corrected for spherical aberration, but de- 

 liberately uncorrected for chromatic aberration, and record the 

 negative of the fluorescence, by taking photographs, in which the 

 fluorescent particles would appear absorbing. But it would be, of 



