VERTICAL ILLUMINATORS, METALLURGICAL MICROSCOPES 97 
merits not found in the earlier models of this valuable instru¬ 
ment and entitles it to be classed among the best instruments 
of the LeChatelier 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 h 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 h), 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. 
