392 JAMES HILLIER 



men point. However, this additional information can be used only 

 with caution since there are many reasons for its being unreliable. 

 Obviously, the information provided in an electron microscope image 

 is not statistical in nature. This is in contrast to the information 

 provided by practically any other kind of scientific instrument. 

 By its very nature, the electron microscope is an instrument for ex- 

 amining heterogeneous samples. While it can examine homogeneous 

 materials, it seldom can provide more accurate information than can 

 be obtained by other techniques. 



B. FIELDS OF APPLICATION OF ELECTRON 



MICROSCOPY 



1. Introduction 



Electron microscopy has made it possible to observe the structure 

 of solids in the range of dimensions from 1 millimicron to 1 micron. 

 It is unfortunate that such a direct and simple statement, accurate 

 though it may be, gives no suggestion of the true magnitude of the 

 role that electron microscopy can play in any science that involves in 

 some way the structure of solid materials. In fact, to this writer, it 

 appears that there are few problems in chemistry, physics, metallurgy, 

 mineralogy, geology, biology, medicine, etc. in which the electron 

 microscope cannot be used. At the same time it is obvious that the 

 electron microscope does not yet play such an important and wide- 

 spread role in general science. The reasons for this are also quite 

 clear. The first of these is the lack of information among the workers 

 who might make use of an electron microscope as to its capabilities 

 and limitations. The second is the fact that early difficulties en- 

 countered with the instrument and with some of the associated 

 techniques have caused the more conservative research workers to 

 wait until those diflRculties have been overcome. On the practical 

 side, one of the most important controlling factors in the general use 

 of the electron microscope has been, as already mentioned^ the lack 

 of suitable techniques of specimen preparation. 



At the present time, a discussion of the general problem of preparing 

 electron microscope specimens is probably the best means of providing 

 the reader with an evaluation of the present capabilities of the 

 instrument. 



