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BELL SYSTEM TECHNICAL JOURNAL 



some definite engineering problem involving telephone apparatus. 

 As the useful range of microscopic vision is extended farther and 

 farther into the realm of higher magnifications, a more exact knowledge 

 of materials is obtained and the effect is learned of physical and 

 chemical forces acting to destroy or to build. 



It has been conceded quite generally that about 1,.500 diameters 

 of magnification represents the limit of useful magnification. As 

 previously stated this is a much disputed question. Laboratory 

 studies, painstakingly carried out over a period of se\-cral years, have 



^r 



Fig. 26 — Various types of eyepiece and stage micrometers used in connection witli 

 the microscope to obtain the dimensions of microscopic objects. 



accomplished impro\cmetits in technique and in precision of adjust- 

 ment of the equipment which ha\e shown that remarkable resolution, 

 depth of penetration and clearness can lie attained in the case of 

 metallurgical specimens, at extremely high powers. There seems 

 little reason to doubt that our knowledge of metals can be augmented 

 very materially by studies of their structures at high powers. 



