exterior tube, being careful o f the circular hole in the exterior
one. Nothing now remains to be done but to adjuft for the
focus, which is effected by pufhing down the tube T V till the
object appears diflinct.
The inftrument may be ufed in two ways for tranfparent ob-
je fts ; firfl, in a vertical pofition, when the light is to be thrown
on the objeft by the mirror L M ; or it may' be examined by
looking up direftly at the lighfr; in the latter cafe the mirror
muff be taken away.
In viewing opake objefts the mirror is o f no u fe; as much
light as poflible muff be let fall on them through the circular
holes o f the tubes.
- i
Any objeft may be viewed by firfl; pufhing the tube I R, and
then bringing the tube T tout’s focal diftance from the objeft.
A D escription of those Parts of a Microscopical
A pparatus, which are delineated in Plate IX.
A and B reprefent the brafs cells which contain the magnifiers
belonging to the different kinds o f compound microfcopes.
The magnifiers are fometimes contained in a Aider like that which
is delineated at Fig. 3, Plate V . The lenfes o f A and B are confined
by a fmall cap ; on unfcrewing this, the fmall lens may be
taken out and cleaned. The magnifiers A of the lucemal microscope
are fo contrived, that any two o f them may be fcrewed
together, by which means a confiderable variety o f magnifying
power is obtained.
To
T o get at the lenfes in the Aider, Fig. 3, Plate V. take out the
two fcrews which hold on the cover.
C, Plate IX. reprefents the general form o f the Aider-holder.
It confifts o f a cylindrical tube, in which an’ inner tube is
forced up by a fpring. It is ufed to receive the ivory or any
other Aider, in which the tranfparent objefts are placed; thefe
are to be Aid between the two upper plates : the hollow part in
one o f the plates is defigned for the glafs tubes. '
D, the condenfing lens and it’s tube, which fits into the Aider-
holder C, and may be moved up and down in it. When this
piece is puflied up as far as it will go, it condenfes the light o f a
candle, which is rellefted on it by the plain mirror o f the compound
microfcope, and fpreads it uniformly over the objeft; in
this cafe it is beft adapted to the fhalloweft magnifiers. I f the
deeper lenfes are ufed, it fhould be drawn down, or rather removed
further from the objeft, that it may concentrate the light
in a fmall compafs, and thus render it more denfe. The con-
denfmg lens is fometimes fitted up differently, but the principle
being the fame, it will be eafy to apply it to ufe, notwithftanding
fome variations in the mechanifm.
E, a brafs cone; it fixes under the Aider-holder. It is ufed to
leflen occafionally the quantity o f light which comes from the
mirror to any objeft.
F, a box, with two Aat glaffes, which may be placed at different
diftances from each other, in order to confine a fmall living infeft.
Q G, a