94 ELEMENTARY CHEMICAL MICROSCOPY 



employed) strike a reflecting mirror V made of " stellite " 

 from which they are reflected to a reflecting prism mounted 

 at the inner end of M whence they are reflected to the eye of 

 the observer. For photography the tube M is pulled out a 

 short distance, thus removing its reflecting prism from the tube 

 T and allowing an unobstructed passage of the rays through N 

 to the ground glass or photographic plate at G. Exposures 

 are made by means of the shutter Sh. 



Since both the coarse adjustment F and the fine adjustment 

 / are attached to the stage support and not to the tube of the 

 microscope, focusing the instrument cannot disturb the align- 

 ment of the radiant. Fine focusing while looking upon the 

 ground glass is accomplished by the Hooke's key KI attached 

 to the fine adjustment. The milled head K2 serves to turn 

 up the burning away carbons, should the arc break or become 

 dim while observations are being made upon the ground glass. 

 To prevent dazzling the eyes by the highly polished specimen 

 a cap with black glass is provided to fit over the ocular of tube 

 M. There is also furnished with the instrument a cap with a 

 tiny central pin hole which fits over the tube M. This device 

 enables the worker to quickly center the radiant with respect 

 to the microscope. 



The full-sized opening (45 mm.) of the stage is cut down for 

 use to 15 mm. by means of a transparent plate glass diaphragm. 



The microscope is normally supplied with square stage only, 

 but a rotating stage can be attached when ordered with the 

 instrument. The mechanical stage which has been adapted to 

 the square stage is awkward, insufficiently rigid and unsatis- 

 factory. 



No device for oblique illumination has yet been developed. 



Each instrument is accompanied by a small pamphlet giving 

 directions for setting up the apparatus and centering the radi- 

 ant. These directions are so clearly written that the veriest 

 tyro should be able to properly manipulate the instrument. 



The Reichert-Holz Metallurgical Microscope. 1 The new 

 model of 1920 embodies may unique features and many improve- 



1 Made by C. Reichert, Vienna, Austria, for the Holz Co., New York, N. Y. 



