Electron microscopes are used to look at objects that would otherwise be too small to be seen optically, for example viruses. Back in 1873 Ernst Abbe had calculated that an optical microscope would never be able to magnify more than 1200 times. The fact is that the wavelength of light is too great for more subtle differences to show.
To overcome this limitation scientists first thought to alter the nature of the light. In the late 19th century experiments were carried out using ultraviolet light, which has a shorter wavelength.
By the 1930s the properties of optical lenses and their effect on light rays was sufficiently understood by scientists for them to draw comparisons with other branches of physics. Ernst Ruska (1906-1988) pioneered the study of electron rays. He identified the fact that such rays could be influenced by magnetic 'lenses' in much the same way as light and they had a much shorter wavelength than even UV light. His work in the late 1920s paved the way for the development of the Polschuh lens...a coil of wire. Then, in 1931, he built a model electron microscope together with Dr Max Knoll at the Technische Hochschule in Berlin. Awarded the Nobel Prize of Physics in 1986, at the age of eighty, he would look back at this work and point out that, 'with this instrument two of the most important processes for image reproduction were introduced-the principles of emission and radiation'.* By 1933 he had developed the first electron microscope to surpass the definition afforded by a light microscope. In the later 1930s he developed customised instruments for industry under the pay of Siemens & Halske whilst his brother, Dr Helmut Ruska, investigated ways of applying the technology to the world of medicine.
A number of Dutch scientists were also involved in developing electron microscopes. J.B. Le Poole produced a prototype in Delft in 1941. Ultimately this design was developed by the electronics giant Philips which came up with the EM100 in 1947, the production team being led by A.C. van Dorsten.
By the end of the Second World War some 35 institutions possessed an electron microscope. Full-scale production began again in Germany from 1949 and resulted in 1954 in the Elmiskop 1, perhaps the first widely used electron microscope.
In Great Britain one of the world's largest producers of electron microscopes was AEI (Associated Electrical Industries) of Trafford Park.
With the advent of the electron microscope this museum's remit for the subject ends. More information about electron microscopes may be found at the Ruska family's memorial site.
As Ruska himself said, the light microscope was the 'first gate' for mankind to gaze at the microcosm and he was prepared to accept that his electron microscope constituted the second gate, but was werden wir finden wenn wir das dritte Tor offnen? ('What will we find opening the third gate?')
*From Nobel Lectures, Physics 1981-1990, Editor-in-Charge Tore Frängsmyr, Editor Gösta Ekspång, World Scientific Publishing Co., Singapore, 1993