heceïïary for this purpofe: for there are many circumfiances
where the images feen may be very fimilar, though originating
from fubftances totally different; it is here the penetration o f the
obferver will be exercifed, to difcover the difference, and avoid
error.*
Hence Mr. Baker f cautions us againft forming an opinion too
fuddenly o f any microfcopic objeft, and not to draw our inferences
till after repeated experiments and examinations o f the objeff,
in all lights and various pofitions; to pafs no judgment upon
things extended by force, or contrafted by drynefs, or in any
manner out of a natural ftate, without making fuitable allowances.
The true colour of objefts cannot be properly determined
when viewed through the deepeft magnifiers; for, as the pores
.and interftices o f an objeft are enlarged, according to the magni-
fying power o f the glaffes made ufe of, the component particles
of it’s fubftance will appear feparated many thoufand times farther
afunder than they do to the naked e y e : it is, therefore, very
probable, that the reflection of the light from thefe particles will
be very different, and exhibit different colours.
Some confideration is alfo neceffary in forming a judgment o f
the motion o f living creatures, or even o f fluids, when feert
through the microfcope; for as the moving body, and the fpace
wherein it moves, are magnified, the motion will alfo be increafed.
IS
* Fontana fur les Poifons, vol. ii. p. 245• •
t Baker’s Microfcope made Eafy, p. 62-
I f an objefit is fo opake as not to fuffer any light to pafs through
it, as much as poflible muft be thrown on its upper furface by
that part o f the apparatus which is peculiarly adapted for opake
objefts.. As -.the apertures iof deep magnifiers are but fmall, and
confequently admit but little light, they are not proper for the
examination of opake objefis : this, -however, naturally leads us
to our fecond head.
Or uihe M a-nAG®M[&nt of the L ight.
The pleafure arifmg from a jufi view of a microfcopic objefil,
the diftinftnefs ofvifion, &c. depend on a due management of
the light, and adapting the quantity of it to the nature ^of the
objea, and the focus of the. magnifier: therefore an objedt
fhould always :be viewed in various degrees of light. For, as
Dr. Hooke'has wellobferved, it is difficult to difiinguilh in Some
objefils between a'prominency and a deprelfion, between a.lhadow
and a black ftain ; and in .colour, between a refleftion .and a
-whitenefs: a truth which the reader .will find fully exemplified.in
the examination of the eye of the libella,.and. other flies, which
will be found to appear exceedingly different in one pofition of
'the-.light from what'they do in another.
' The brightness o f an objea, depends on the quantity (jf light;
the diftinanefs of vifion, on regulating the-quantity to the o b je a ;
for fome will be loft, -and drowned, as it were, in a quantity o f
light that is fcarce fufficient to render another vifible. A ftrong
light may be thrown■ on an.objea various ways; :firft, by means
o f the fun and a convex lens; for this purpofe, place the microfcope
about three * feet from a Southern window; .take a deep
R 2 convex