VERTICAL ILLUMINATORS, METALLURGICAL MICROSCOPES 91 



difficulties and further to permit the examination of fragments 

 of moderate size, the microscope is more conveniently inverted, 

 i.e., constructed with the objective lying below the stage. The 

 alloy can thus be laid upon the stage, polished surface down over 

 the stage opening. It will thus meet the requirement that its 

 etched surface shall lie in a plane normal to the optic axis. 

 Coarse adjustment focusing is accomplished by displacing the 

 stage up or down, the tube of the microscope remaining in a 

 fixed position, assuring no disarrangement of the proper align- 

 ment of the illuminator with reference to the radiant. 



Most of the large metallographs are developments of the type 

 first suggested by Le Chatelier. Two instruments have been 

 selected for illustration as embodying the largest number of good 

 features to the exclusion of those which are distinctly bad. 

 These have been described at length in preference to other 

 valuable instruments since the author has had the opportunity 

 of working with them and thoroughly testing them. 



The Leitz Metallurgical Microscope. This instrument con- 

 sists of the vertical illuminator shown in Fig. 37 applied to a 

 compound microscope so arranged as to lie in a horizontal posi- 

 tion. The general arrangement of its component parts is illus- 

 trated by Fig. 43. An optical bench B carries a series of stands 

 with saddle bases. These stands support the different unit 

 parts of the instrument. The first stand carries a small arc 

 lamp R, a condenser C and a screen E ; attached to E is an iris 

 diaphragm D and a shutter (not shown in the cut) for making 

 the photographic exposures. The next stand supports the com- 

 pound microscope and its accessories; the mechanical stage S/, 

 the illuminator I fitted with iris diaphragm d, the reflecting prism 

 V and the body tube of the microscope M with its ocular; over 

 the ocular is fitted a removable black glass disk b. Coarse adjust- 

 ment of the microscope is obtained by the wheel F which raises 

 and lowers the stage St supported by four pillars; the object to 

 be examined is placed polished side down over the opening of the 

 stage; the rays of light projected by the radiant enter the illumi- 

 nator I, are then reflected upward through the objective and 

 strike the surface of the object; the rays are thence reflected 



