M i c r o s c o p i c a l E s s a y s .
Iflj
116
The two upper plates each contain a magnifying lens, but of
different powers : one o f thefe confines and keeps in their places
the fine point F, the forceps G, and the fmall knife H.
T o ufe this inftrument, unfcrew the upper lens, and take out
the point, the knife, and the fprceps; then fcrew the lens on
again, place the objeft on the ftage, and then move it up or
down till you have gained a diftinft view o f the objeft, as one
lens is made of a fhorter focus than the other; and fpare lenfes,
o f a ftill deeper focus, may be had if required. This little micro-
fcope is the invention of Dr. Withering, and is defcribed by him
in his “ Botanical Arrangements.” It’s, principal merit is it’s,
fimplicity.
C ommon Botanical Microscope,
This little inftrument is reprefented at Fig. 2, Plate VI. It
appears to me preferable to Dr. Withering’s, being equally
fimple, more extenfive in it’s application, and the ftage unincumbered;
though that o f M. Lyonet feems better adapted
than either to the purpofes o f diffe&ion.
A B, a fmall arm, carrying, the two magnifiers, one fixed to
the upper part as at B, the other to the lower part o f the arm at
C ; thefe may be ufed feparately or combined together. The
arm A B is fupported by the fquare pillar IK , the lower end o f
which fits into the focket E of the foot F G ; the ftage D L is
made to Aide up and down the fquare pillar; H, a concave mirror
for reflefting light on the object.
T o
M i c r o s c o p i c a l E s s a y s . 117
T o ufe this microfcope, place the objeft on the ftage, refleft
the light on it from the concave mirror, and regulate it to the
focus, by moving the ftage nearer to or further from the lens at
B. The ivory Aiders pafs through the ftage; other objeas may
be fixed in. the nippers L M, and then brought under the eye-
glaffes ; or they may be laid on one o f the glaffes which fit the
ftage;
The apparatus to this inftrument confifts o f three ivory Aiders,,
a pair o f nippers, a pair of forceps, a fiat glafs, and a concave
ditto, both fitted to-the ftage;.
B o t a n i c a l M a g n i f i e r s .
Since botany has been cultivated with fo much ardor, it has:
been found necefiary to contrive fome very portable inftrument,.
by which the botanift might inveftigate the objeft of his purfuits,
as it rifes before him. Figures 7 and 8, Plate VIII. reprefent
two, the molt convenient of this . kind.
In the cafe, Fig. 8, are three lenfes, g, h, i o f different magnifying
powers, that all turn up and lhut into the cafe.
Fig. 7 contains alfo three lenfes, a, b, d, of different foci, which-
are all made to turn into the cafe, and may be ufed combined or-
feparately.
The three lenfes. in themfelves afford three different magnifying
powers; b y combining two and two we make three more,
the three together make a feventh magnifying power with three
lenfes.