CHAPTER 12 

 POSSIBILITIES OF FUTURE DEVELOPMENT 



THE future development of the electron microscope is likely 

 to proceed in two general directions. One line of develop- 

 ment will aim at a simple, safe, and yet powerful instrument 

 which will be as useful, and probably as indispensible in the 

 routine tests of virus diseases, as the optical microscope is in 

 bacteriological tests. The simplified R.C.A. electron microscope 

 can be considered at present as the nearest approach to this 

 ideal, but its resolution limit of about 100 A still falls rather 

 short of the limit of about 20 A which appears desirable. 



The second line of development will aim at a reduction of 

 the resolution limit considerably below 20 A, and to create a new 

 tool for fundamental investigations in physics, chemistry, and 

 biology. A discussion of these possibilities will be attempted 

 here, which will be divided into two parts. First, it will be 

 convenient to discuss possible improvements in the uncorrected 

 type of microscope, that is. improvements more or less along the 

 line which has led to the present stage. The second part is a 

 survey of the possibilities for creating electron optically cor- 

 rected microscope objectives. 



Possible Improvements in the Uncorrected 

 Electron Microscope 



In chapter 7 we have derived equation (24) for the resolu- 

 tion limit of the uncorrected microscope, which results from the 

 optimum balance of spherical aberration and dififraction. We 

 write this now, somewhat more conveniently, 



d,^ = ysoc^f^yy \\ (24b) 



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