GENERAL DIRECTIONS. 
be the position of the sun in the heavens, such a position can 
always be given to the plane of the mirror, that the light may be 
reflected along the axis of the microscope. 
The great condensing lens is set in the larger end of the conical 
tube T, and the lesser in the end of the cylindrical tube t' ; the 
latter tube being moved within the former by an adjusting screw, 
which appears at its side. By the second condensing lens, the light 
is collected upon the opening in the slide, which is held between 
two plates n, pressed together by spiral springs. 
The tube t’ consists of two parts, one moving within the other, 
like those of the telescope. 
The amplifying lenses are mounted in a brass ring, K, carried by 
the upright piece, I, so that its optical axis shall coincide with 
that of the illuminating apparatus. This optical part can be 
moved to and from the object, by means of a rack and pinion, F, 
attached to the piece H, which slides in the box G. 
The structure and principle of the instrument being understood, 
it only remains to explain the method of using it. 
11. The room in which the operations are conducted should 
have suflicient depth to allow the space between the microscope 
and the screen, which ^s necessary for the formation of an image 
of the required magnitude. This space will vary with the mag¬ 
nifying power required, but in general 10 or 12 feet beyond the 
nozzle of the instrument is sufficient. The room should be rendered 
as dark as possible, to give effect to the image, which, however well 
Fig. 3. 
illuminated, is always incomparably less bright than would be 
objects receiving the light of day. The window-shutters should 
therefore be carefully closed, and all the interstices between them 
stopped. If the room be provided with window-curtains, they 
should be let down and carefully drawn. In a word, every means 
should be adopted to exclude all light, except that which may 
enter through the microscope. 
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