100 



ELEMENTARY CHEMICAL MICROSCOPY 



In the Stead instrument, Fig. 47, the body tube is supported 

 upon three adjustable legs. Focusing is done by hand by rais- 

 ing or lowering the tube in a sleeve. When in focus the instru- 

 ment is held in place by a clamping screw C. A vertical illumi- 

 nator of the disk type forms an integral part of the instrument. 1 

 The radiant in this case consists of a tiny incandescent electric 

 lamp enclosed in a sleeve at right angles to the illuminator mount- 

 ing. As the instrument is intended for low magnifications only, 

 no fine adjustment is provided. 



A somewhat similar idea in illum- 

 inator construction is found in the 

 Tassin metallurgical microscope. 2 

 In this instrument, Fig. 48, we find 

 the illuminator of the form already 



FIG. 49. Leitz Metallurgical Microscope. 



described on page 84, Fig. 39, the radiant being either an elec- 

 tric or an acetylene lamp. The microscope itself has no substage 

 but is mounted upon a heavy base with central opening and pro- 

 vided with four large leveling screws. 



The third type of instrument is illustrated by the Leitz metal- 

 lurgical microscope, Fig. 49. Here we have a compound micro- 



1 See Stead, Work Shop Microscopes. J. Roy. Micro. Soc. 1909, 20, 22. 



2 For its application see Tassin, The Microstructure of Steel Castings, J. Ind. 

 Eng. Chem., 5 (1913), 713. Metallography as Applied to Inspection, J. Ind. 

 Eng. Chem., 6 (1914), 95. 



