140 



The Electron Microscope 



source. 



condenser. 



Qbfecb. 

 objective,. 



diFFractec( beorvi 



shield 



Phob^plabe, 



Fig. 51 



lens arrangement a very strongly reduced image of the electron 

 source or the cross-over is focused on a small part of the speci- 

 men. The transmitted electrons, some of which have suffered 

 energy losses, are refocused on the slit of an electron velocity 

 analyzer. This is of the Jialf-circle type introduced by Ramsauer. 

 A homogeneous magnetic field at right angles to the beam bends 

 the electron trajectories to circles, and it is well known that the 

 slit will be approximately focused on a photographic plate which 

 is arranged at 180° from the slit, in radial direction. If operated 

 with the extremely constant voltages and currents produced by 



