Photomicrography and Technical Microscopy in 

 Its Application to Telephone Apparatus 



By FRANCIS F. LUCAS 



Note — The following paper may be considered as introductory to the 

 subject of photomicrography. Doubtless everyone is casually familiar 

 with photomicrographs of the crystalline structure of various metals. 

 The application of this branch of the optical art to the study of metals 

 is very important in the design and manufacture of telephone apparatus 

 but its importance in telephony is more far-reaching than in the study of 

 metals alone, \arious of these applications are suggested by the illus- 

 trations reproduced in the .Appendix of this article. — Editor. 



Introdictiox 



BY photdniicrograpliy is meatit the adaptation of photography 

 to microscopy, or the art of photographing a magnified image. 

 The scope of the art embraces the reproduction of images ranging 

 from natural size up to magnifications of several thousand times, 

 the degree of magnification being expressed in terms of diameters. 

 It will be seen that the image is not always magnified but in some 

 instances may be at a 1 :1 ratio or when large subjects are being 

 photographed, at an actual reduction in size. Such low-power work 

 is often spoken of as gross photography but so far as the equipment 

 and technique of treatment is concerned it is low-power work. 



Low-power work may be considered as treating with magnitudes 

 from 1 to about 30 diameters. Medium-power work deals with 

 magnifications from about 30 to about 500 diameters, and high-power 

 work extends from 500 diameters upward. The limit of useful 

 magnification is a much disputed question. It is sometimes contended 

 that 1,500 diameters represents about all that is worth while, but 

 the fact that very few pictures are published which exceed 1,500 

 diameters in magnification would lead to the conclusion that either 

 the limit is from 1,000 to 1,500 or else the art has not been developed 

 to the state where substantial gains result by going higher. This 

 matter will be considered at greater length below. 



Gkxkral Discission of App.xr.vti's 



The reason that photomicrography is grouped under three classifi- 

 cations according to magnification, is because the apparatus used in 

 each case is quite different and because the preparation of the stibjcct 

 and its treatment also diflfer. In fact for low-power work the micro- 

 scope often may be dispensed with entirely, the lens being secured 

 directly to the camera; in other cases, the microscope serves only as a 



100 



