Possibilities of Future Development 



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potential lens is connected with the cathode as usual, whereas 

 the outer electrode, preferably earthed, is formed by. the pole 

 pieces of the magnetic lens. The object is placed outside this 

 lens, shielded from the strong electrostatic fields by an apertured 

 diaphragm. The focal length of this first lens is supposed to 

 be of the same order as in present-day microscopes, i.e., about 

 0.5 cm for 60 kev electrons. 



Fig. 40. Potential and trajectories in electrostatic lenses 



The space charge lens is essentially a cylindrical magnetron, 

 but with the important difference that it contains no axial 

 cathode. Its main parts are a long coil, which produces, at least 

 in the middle part, a nearly homogeneous magnetic field, a 

 tubular anode or sheath electrode *'A," and a cathode "C," 

 which is a filament, bent to a coaxial circle. The currents are 



