54 Description of an improved Microscope. [Jan. 
inches. This compartment is made pretty much like a camera 
obscura, except that the end 3 can be removed at pleasure. 
On the top of this box, a piece of brass is sunk into the wood 
close to the hinge of the camera, as seen at x. The body of the 
instrument screws into this. The brass bar, 00, is attached to 
the box by means of the stand, ¢, made, as seen in the plate, 
_ attached by the two screws, 11, to the sheath which carries the 
arm, cc. ‘This stand is again attached to the box by the screw, 
6, which passes thraugh the projecting part, y, and fixes mto a 
piece of brass sunk into the top of the box. This projecting 
part has a groove in it, by means of which the instrament moves 
backwards or forwards, and places the body of the microscope 
either in its situation as in fig.,2, or mm that represented at fig. 1, 
according as a transparent or opaque object is to be examined. 
In fig. 2, it is mounted for viewing a transparent body ; the reader 
will observe the mirror, S (fig. 1), removed, and in its place the 
condensing lens, «, two inches diameter, four inches focus, sub- 
stituted. The moveable stage, G, is now attached, and a slider 
holder is fixed m it by means of the little notch. The body ofthe 
instrument is now seen much further from the brass. bar than 
‘before, being placed in the axis of the mirror and lenses. The 
height of the stand, 6, must be made to correspond exactly with 
the body, so that the arm, cc, may just coincide with its sheath: 
in my instrument it is two inches high above the box ; but it 
might be made something higher, and the brass bar, 00, might 
be proportionally shortened, which would make the instrument 
look better. The body used in fig. 2 is not the same as that in 
fig. 1, being precisely similar to that of a common compound 
microscope in its optical principle, except that the brass buttons 
made to screw on at its end heve much smaller apertures than 
those generally made; likewise a piece of tube, a, is made to 
slide up and down, which is used to slip over the brass button 
down to the slider-holder ; and thereby exclude all rays from the 
instrument which do not come directly through the stage ; this 
much improves the vision of many transparent objects : it can be 
used or not, as is most eligible. 
It will no doubt appear strange that I should have rejected 
this kind of microscope in fig. 1], and employed it here for view- 
ing transparent objects; but there are reasons for every thing. It 
is a curious fact, which I am not sufficiently skilled in optics to 
fathom, that the body, A B, fig. 1, though it shows opaque 
objects perfectly achromatic, does not seem to me to show tran- 
sparent ones so, which this microscope does. Besides, I have 
not forced it to magnify so much as the transparent body does, 
because, opaque objects being seldom or never flat, only a point 
can be in the focus at a time, the rest being all confusion, and 
this in proportion to the magnifying power; so that a person does 
not know what he is looking at. A transparent body, being 
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