134 



PROGRESS IN MICROSCOPY 



determine the grain size and to devise differences that may be cor- 

 related with constituents of various hardness numbers. 



F. W. Cuckow showed that phase-contrast and electron microscopy 

 images are closely alike: in a chrome-nickel steel the phase-contrast 

 dark areas are correlated with the dark areas of an impression observed 

 in the electron microscope and hence, to hollows in the cross-section. 

 Cross-sectional differences in levels of flat metallographical sections 

 are further magnified by etching. F. W. Cuckow and D. McLean 

 showed that moderate etching affords much more detailed images in 

 phase-contrast microscopy. 



Therefore, phase-contrast microscopy is a valuable tool in metallo- 

 graphy and, in general, when investigating non-diffusing reflecting 

 objects. 



The Jupnik, Osterberg and Pride phase microscope (American Optical 

 Company) 



The object P is illuminated (Fig. 4.8) by a vertical illuminator set 

 next to the objective Oi, as in ordinary reflected-light microscopes. 



T p 



Fig. 4.8. Jupnik, Ostcrherg and Pride device. 



The source F, which is, in fact, a diaphragm upon which is imaged 

 a lamp filament, may be shaped either as a ring or a slit. 



In order not to over-elaborate Fie. 4.7, a slit in shown. The light. 



