HISTORY OF ELECTRON OPTICS 



to improve the performance of the electron two-stage magnification. Around 1941, Hil- 



microscopes. These were twofold — ^one was lier attempted to use a compound projection 



building new microscopes of which a few lens. Three-stage magnification was intro- 



merit brief mention: The- instrument by duced in 1942-43 by Marton. This idea was 



Scott and iVIcMillen (1936) for the emission- taken up, probably independently, late in 



type observation of biological subjects. This 1944 by Ruska and von Borries in a patent 



was the first compound emission microscope application, and in 1944-46 by Le Poole. Le 



in America. Second, the instrument of Mar- Poole also introduced selected area diffrac- 



tin, Whelpton, and Barnum in England tion as an adjunct to electron microscopy, 



(1937) which sparked the British work in this using a three-stage arrangement, 



field; and the third, the new instrument of The postwar years have seen the rapid 



Ruska and von Borries (1938). This last in- development of commercially available 



strument paved the way to the fii'st commer- models in different countries. An important 



cial model, completed in 1939. There were contribution to the present-day development 



also advances in applications. In 1937, Mar- was recognition of the role of lens astigma- 



ton had taken the first bacteriological pic- tism by Hillier and Ramberg in 1946. Recog- 



tures. These were followed in 1938-39 by nition of this defect led, in the ensuing years, 



improved bacteriological pictures by Ruska to the development of different types of 



and collaborators. The first virus pictures electrostatic or magnetic stigmators and 



were obtained by Helmut Ruska, brother of produced the present high resolving power 



Ernst Ruska, in 1940. of modern instruments. The existence of the 



In 1938-39, some papers also appeared high resolution transmission type micro- 

 by von Ardenne analyzing some of the de- scope stimulated the development of several 

 fects of the microscope. The most important related instruments. First of these was the so- 

 single item probably was an analysis of the called scanning microscope proposed by von 

 alignment defects on the basis of which von Ardenne in 1938, followed by further im- 

 Ardenne built a very complicated and highly provements by Zworykin, Hillier, and Sny- 

 successful instrument establishing a tem- der in 1942. In 1939, the electron shadow 

 porary world record of 30 A for resolving microscope was proposed by Boersch. In the 

 power. Coincident with that development same year, 1939, von Ardenne proposed the 

 was development also of the first electro- X-ray shadow microscope. The practical de- 

 static microscope by Mahl and Boersch, as velopment of this instrument had to wait 

 well as the development of the fu'st Canadian until the 1950's when Cosslett and Nixon 

 microscope by Burton, Prebus and Hillier. built the first working instrument. Another 

 This was followed by the development of the related instrument is the microprobe ana- 

 first American commercial model — -the RCA lyzer of Castaing first described in 1951. Ion 

 Type A was completed by Marton in 1940, microscopes are another group of derived 

 followed by RCA Type B in 1941 by Zwory- instruments. The first attempt was made 

 kin, Hillier, and Vance. These two last- with lithium ions in 1947 by Boersch, In 

 named instruments were the first ones to use 1949, Magnan and Chanson published the 

 highly regulated electronic power supplies, first description of a proton microscope. 

 The German work relied on the stability of The 1932 attempts of Knoll and Ruska, as 

 storage batteries to achieve the required well as Briiche and Johannsen, in emission 

 constancy of the magnetic lenses. microscopy has been mentioned earlier. The 



Japanese work on electron microscopy resolving power of these emission micro- 

 started in 1939 partly by Higashi and Tani, scopes was quite poor, and no progress was 

 also by Tadano. made until Recknagel in 1941 developed a 



All the above-described instruments used theory of immersion objectives. In 1942, 



157 



