138 



The Electron Microscope 



exposures than the conventional type of diffraction camera, with 

 parallel beams, collimated by pinholes. 



ELECTRON 

 SOURCE 



CONDENSER 

 LENS 



OBJECTIVE 

 LENS 



PROJECTION 



LENS 

 Limiting Aperture 

 of Focusing lensj^ 



SPECIMEN 



FOCUSING 

 LENS 



SCREEN 



Fig. 49. Electron optical arrangement of R.C.A. diffraction adapter 



Figure 50 shows an example of a diffraction pattern and 

 micrograph obtained w'ithin a few minutes of one another. In 

 many cases, especially if one has to deal wath mixtures of sub- 

 stances, it would be desirable not only to shorten this time, but 

 also to have means for identifying the particle which produced 

 the diffraction pattern. Von Ardenne and collaborators "^ have 

 constructed a universal electron microscope in which a very fine 

 electron probe can be directed at different parts of the specimen 



