O f the necessary Preparation of the M icroscope
for O bservation. '
We have in the laft chapter explained thofe particulars that
conftitute the difference o f one microfcope from another, and
fliewn how each inftrument is to be ufed, and how the feveral
parts are to be applied to it. We fhall now proceed to give fome
general direftions applicable to every microfcope. The obferver
is therefore fuppofed to have made himfelf mafter o f his inftrument,
and to know how to adapt the different parts o f the apparatus
to their proper places.
The firft circumftance neceffary to be examined into is,
whether the different glafles belonging to the microfcope are perfectly
clean or riot; i f they are not clean, they mull be taken out
and wiped with a piece of wafti leather, takirig care at the lame
time not to foil the furface of the glals with the fingers: in replacing
the glafles, you mull alfo be careful not to lay them in
an oblique fituation.
The objedt Ihould be brought as near the center o f the field of
view as poflible, for there only will it be exhibited in the greateft
perfection.
The eye Ihould be moved up and down from the eye-glafs of
a compound microfcope, till you find that fituation where the
largeft field and moll diftinft view o f the objefl is obtained.
Every perfon ought to adjuft the microfcope to his own eye, and
not depend upon the fituation it was placed in by another.
Care muff: be taken not to let the breath fall upon the eye-
glafs, nor to hold that part of the body o f the micrc fcope where
the glafles are placed with a warm hand, becaufe the damp that
is expelled from the metal by the heat will be attracted and con-
denfed by the glafles, and obltruCt the fight of the objea.
The obferver Ihould always begin with a fmall magnifying
power; with this he will gain an accurate idea of the fituation and
conneaion of the whole, and will therefore be lefs liable to form
any erroneous opinion, when the parts are viewed feparately by
a deeper lens. By a fhallow magnifier he will alfo difcover
thofe parts which merit a further inveftigation.
Every objea Ihould, i f poffible, be examined firft in that
pofition which is moll natural to i t : if this circumftance is neg-
leaed, very inadequate ideas o f the ftruaure of the whole, as
well as o f the conneaion and ufe o f the parts, will be formed.
I f it be a living animal, care mult be taken not to fqueeze, hurt,
or difcompofe it.
There is a great difference between merely viewing an objea
by the microfcope, and inveftigating it s nature: in the firft we
only confider the magnified reprefentation thereof, in the fecond
we endeavour to analyfe and difcover it’s nature and relation to
other objeas. In the firft cafe, we receive the impreflion o f an
image formed by the affion o f the glaffes; in the fecond, we form
our judgment by inveftigating this image. It is eafy to view the
image which is offered to the eye, but not fo eafy to form a judgment
o f the things that are feen ; an extenfive knowledge o f the
- fubiea, great patience, and many experiments, will be found
1 ° r neceffary