30 
MECHANICAL PORTION OF THE MICROSCOPE. 
lever, which gives to the stage a delicate upward movement. 
Two sliding clips retain the object on the stage. 
The stage, which is three by four inches, is so constructed 
that it can be moved smoothly and steadily in every direction, 
the object appearing to follow the motions of the hand upon 
the lever. This movement of tlie stage gives great facility for 
tracing every part of the slide in the search for delicate ob- 
jects, and enables the observer to follow with ease the motions 
of living animalculse, even with high powers. Beneath the 
stage is a circular plate carefully centered and adapted for re- 
ceiving accessory apparatus. The mirrors, plane and concave, 
(the latter two inches in diameter,) are so mounted as to have 
a free and steady motion in every direction. By means of an 
arm, the mirrors can be thrown far out from the axis of the 
microscope, so as to give mvy oblique light for illuminating the 
object. 
This instrument has a graduated draw-tube^ by which the dis- 
tance between the objective and eye-piece can be considerably 
increased. This increased length produces a proportional in- 
crease of the magnifying power, and thus often greatly aids 
in ascertaining the value of micrometer graduations. (See 
71, 72.)* 
49. Stage Movable by Rack and Screiv. American 
microscopists generally prefer our form of stage, movable by a 
lever. The instruments which we keep on hand are, therefore, 
usually furnished with this form of stage. But we are accus- 
tomed to make to order a stage movable in two rectangular 
directions, by rack and screw. 
* This instrument is often made with a plain stage, which considerably re- 
duces the expense. It can also have added the revolving motion of the stage, 
as shown in the next figure. Baileys’ Indicator Stage can be applied to this in- 
strument, if desired, instead of the stage here shown. The use of cast-iron, for 
the base and arm of the preceding instruments, has been adopted to bring the 
prices within the most reasonable limits. This arrangement does not, in any man- 
ner, diminish the efficiency or beauty of the instruments. The parts made of iron 
are carefully smoothed and neatly japanned, and give a pleasing contrast of color 
with the other parts, which are of brass. But when specially ordered the base 
and arm are also made of brass, at a reasonable addition to the price. 
J. & W. GRUNOW & GO’S ILLUSTRATED 
