VERTICAL ILLUMINATORS, METALLURGICAL MICROSCOPES 97 



ments not found in the earlier models of this valuable instru- 

 ment and entitles it to be classed among the best instruments 

 of the LeChateiier type. As will be seen in Figs. 42, 43, 

 44, it consists of a heavy optical bench B carrying illuminating 

 devices, a microscope and a camera. The camera is also arranged 

 so as to permit low power photography under either axial or 

 oblique illumination. 



The microscope A is built upon a very heavy base sliding 

 upon the optical bench B. From the center of the base rises 

 a heavy pillar carrying the coarse adjustment F which serves 

 to raise or lower the stage S in focusing the image of the speci- 

 men M. The microscope proper, supported by the pillar P3, 

 consists of an observation tube T, a projection tube C, and ver- 

 tical illuminators b attached to a central prism chamber, into 

 the upper opening of which is fitted the objective O. A clamp 

 t holds the stage securely in place after the image has been 

 focused and guards against displacement when heavy objects 

 are lying upon the stage. Attached to the stage is a scale 

 moving past the indicating pointer I. This scale is marked 

 with the positions which the stage will occupy when each of 

 the different objectives supplied with the instrument are in turn 

 in focus. This indicating device for quickly adjusting the focus 

 is a great convenience since it enables the worker to at once find 

 the focal plane of any objective and also shows at a glance 

 which objective is in use. 



A clamp or tongs c is supplied with the instrument to facilitate 

 inserting and removing objectives. The objectives are in special 

 mounts and are not threaded, hence standard mount objectives 

 cannot be used on this instrument. 



The prism chamber is shown in section in Fig. 45. The 

 illuminating rays from the radiant (Mazda lamp or arc lamp) 

 are reflected by the prism P (in the tube b), pass through the 

 objective O, and striking the polished surface of the object M 

 are again reflected through the objective to the prism Pi and 

 thence to the eye of the observer at the end of the tube T. A 

 turn of the milled head K through 90 sends the rays through 

 the tube C and thence to the photographic camera. 



