30 The Electron Microscope 



References to comprehensive accounts may be found in the bibU- 

 ography.^^ The supermicroscope, however, has become a success 

 only in the last years, and there are reasons to believe in its con- 

 siderable further development. 



The transmission type or supermicroscope is called magnetic 

 or electrostatic according to the type of its objective. The mag- 

 netic microscope is the older, and for the time being the more 

 successful type. Its official birth year is 1932, as in this year 

 M. Knoll and E. Ruska published their first paper ^"^ on it. The 

 first successful electrostatic microscope was constructed, in 1939, 

 by H. Mahl.18 



In the ten years which followed the first publication by Knoll 

 and Ruska the magnetic microscope has changed little in prin- 

 ciple, but every detail was perfected by long patient work, with 

 the result that the performance of the instrument was improved 

 more than a thousand times. It is almost impossible to do full 

 justice to work of this kind. The enumeration of principles, 

 means, and devices is likely to leave out just those difficulties 

 which it took the experimenters all their energy and patience to 

 overcome. Only those who have worked with large and compli- 

 cated experimental apparatus know what a challenge they are to 

 the "cussedness of objects," and how often those difficulties which 

 it took most time to overcome appear afterwards too trivial even 

 to be mentioned in the publications. 



Among the workers to whom the present development of the 

 magnetic supermicroscope is mostly due may be mentioned : 

 M. Knoll, E. Ruska, B. von Borries and j\I. von Ardenne, in 

 Germany; E. F. Burton, J. Hillier, W. H. Kohl, A. Prebus, 

 A. W. Vance and Y. K. Zworykin, in the United States and 

 Canada ; L. Marton, in Brussels and later in the United States ; 

 and L. C. Martin, in Britain.* The development of the magnetic 

 microscope to the commercial stage owes most to two great elec- 

 trical firms : Siemens and Halske, of Berlin, and the Radio Cor- 

 poration of America. In 1935, Siemens established a special 



* The first British electron microscope was constructed by Metropolitan 

 Vickers Electrical Co., Ltd. in 1936.28 



