THE MICEOSCOPE. 
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parallel columns united by a solid cross-piece ; the lower column 
(suspended between the pillars of the stand) bearing the illumi- 
nating- mirror, stage, rack-work, &c., the upper column being 
the body or tube of the optical instrument, with its objective 
and eye-piece. Fixed to the middle of the lower column is the 
stage, a flat table, having an aperture situated immediately in a 
line with the tube of the microscope, for the admission of light 
from below, which is thrown up by the mirror. The glass 
slide containing a mounted transparent object which is to be 
viewed by transmitted light, is placed upon this stage, being- 
secured from slipping out of its position by a movable ledge 
which is readily adjusted so as to secure beneath the object- 
Fig. 2. 
glass the particular portion of the object which it is desired to 
examine. This stage is sometimes furnished with a pair of milled- 
heads which move it forwards or sideways at pleasure, so that 
any moving object may be kept in the field without the 
necessity of touching the slide or cell containing- the object. 
Immediately beneath the stage is a circular plate called the 
diaphragm, with perforations of various dimensions, from the 
size of a pin’s head to that of the aperture in the stage itself. 
These openings regulate the amount of light admitted, 
very transparent objects being scarcely discernible in the full 
glare of light admitted through the large apertures, which, 
however, are necessary for the examination of objects of a more 
opaque character, which require all the light obtainable. At 
the foot of the column is the concave mirror, which, being 
