Brief history of transmission electron microscopes
It remained well into the 20th century before resolution greater than that of the light microscope could be achieved. This depended upon employing illumination with a vastly shorter wavelength than that possible in the light optical range. Electrons, discovered by the British physicist, J.J. Thompson, in 1898, were shown by L. deBroglie in 1924 to possess wave properties nearly a thousand times shorter than that of visible light. Since it was recognized that the resolution of the light microscope was limited mostly by the wavelength of visible light, electrons seemed to offer an outstanding possibility for vastly improved resolution (and therefore also magnification).
With the work of physicists, such as H. Busch, M. Knoll and E. Ruska from 1925 through 1934, strong electromagnetic lenses were developed that enabled electron beams to be focused in much the same manner as glass lenses direct the pathway of visible light. In fact, the basic design of early transmission electron microscopes (and even today's instruments), follow similar optical pathways as that of light microscopes. Electrons, however, can be deflected by the presence of air; hence the electron microscope needed to have a vacuum system for the pathway of the electron beam.
The first electron microscope in North America, built in 1937 in Toronto, Ontario, Canada can be seen at the top.
A modern transmission electron microscope with many refinements is shown at the bottom. Although appearing quite different, it uses essentially the same optical plan as the instrument shown at the top.
