the places which correfpond to the two holes through which the
fcrew is to pafs ; take away the microfcope, and bore two holes
at the marked places, fufficiently large to let the milled fcrews
pals through them.
Thefe fcrews are to pafs from the outfide o f the fhutter, to go
through it, and being then fcrewed into their refpeftive holes in
the J'quare plate, they will, when fcrewed home, hold it fall
againft the infide o f the Ihutter, and thus fupport the microfcope.-
Screw the conical tube A B C D to the circle a be, and then
Aide the tube G of the opake box into the cylindrical part C D
E F o f the body, if opake objeas are to be examined ; but if they
be tranfparent objefts you mean to Ihew, then place the tube A
within the tube C D E F.
T h e room is to be darkened as much as poffible, that no light
may enter but what paffes through the body o f the microfcope ;
for, on this circumftance, together with the brightnefs o f thefun-
Ih-ine, the perfeftion and diftinftnefs o f the image in a great mea-
fure depend. I
I {hall firft oonfider the microfcope as going t o b e u s e d f o r
o p a k e OB JE C T S , l. Adjuft the mirror N O P, fo as to receive the
folar rays, by means o f the two finger fcrews or nüts, Q, R ; the
firft, Q, turns the mirror to the right or left ; the fécond, R, raifes
or deprefles it : this you are to do till you have refleâed the fun s
light through the lens at A B , ftrongly upon afereenof white paper,
placed at fome djftance from the window, and formed thereon
a round fpot of light. An unexperienced obferver will find it more
M ic ro s co p i c a l ' E s s a y s . 97
convenient to obtain the light, by forming this fpot before he puts
on either the opake box, or the tooth and pinion microfcope.
Now put in the opake box, and place the objeft between the
plates at H ; open the door i k, and adjuft the mirror M, till you
have illuminated the objeft ftrongly. I f you cannot e fie cl this by
the fcrew S, you muft move the fcrews O, R, in order to get the
light reflected ftrongly from the mirror N O P, or the mirror M,
without which the latter cannot illuminate the objeft.
The objeft-being ftrongly illuminated, fhut the door ik , and
a diftinft view o f the object will foon be obtained on your fereen,
By adjufting the tubes V X, which is eftefted by moving them
backwards or forwards.
A round fpot of light Cannot always be procured in northern
latitudes, the altitude of the fun being often too low; neither can
it be obtained when the fun is direftly perpendicular to the front
■ of the room.
As the' fun is continually changing it’s place, ft will be necefiary,
in order to keep his rays full upon the objeft, to keep them continually
direfted through the axis of the inftrument, by the two
-fcrews Q and R.
T o view tranfparent objefts, remove the opake box, and infert
the tube Y o f Fig. 2, Plate V. in it’s place; put thé Aider, Fig. 3,
Plate V. into it’s place at n, and the Aider, with the objefts between
the plates, at m ; then adjuft the mirror NOP, as before
direfted, by the fcrews Q, R, fo that the light may pafs through
N the