Microscopy has always been concerned with the observation of samples in their natural states. The earliest instruments, optical microscopes, did not interfere with the samples which were under observation due to the pervasive presence of visible light in the normal evolution of these entities. Man and science persisted in this direction until Ruska in 1933 invented the electron microscope and the real world changed forever (see MSA Rudenberg for an enlightening description of the early days of man's understanding of the electron and the subsequent invention of the electron microscope). The earliest electron beam instruments were single vacuum chamber entities. As single chamber designs, every element in the optical path was under vacuum. These included the electron gun, the lens and coils, recording film, and of course, the specimen itself. The purpose of the vacuum was quite obvious...to eliminate the scattering of the electrons due to the presence of gas.