Limit of Electron Microscopy 



133 



posed to circle, which is 1.064 A. In an electron micrograph the 

 missing electrons would produce a deficit inside a disk of ap- 

 proximately this diameter. As the missing electrons are mostly 

 inelastically scattered electrons which constitute also more than 

 90 per cent of the total scattering, the contrast will be about 



(-1 — .) =0.08 which falls just a little short of 10 per cent. 



We can therefore say that in an electron microscope with lenses 

 perfect as regards spherical aberration but uncorrected for 

 chromatic aberration, a hydrogen atom would be just below the 

 limit of visibility. We see also that the reason for this is not so 

 much the smallness of the hydrogen atom, but rather that it is 

 too large for the electric charges which it contains, in other 

 words, its density is too low. 



x/0 cm 





Apparent at am diameber 



\ S Limit oFeFF.opertufe 



BY THOMAS- FERMI ATOM. 



Fig. 47 



