76
T h e upper part f g r s o f the ftage, is to be raifed or lowered
occafionally, in order to make the center o f the objeCt coincide
with the center o f the lens at O.
T o delineate objeCis, the grey glals mull be placed before the
large lenfes ; the picture o f the object will be formed on this glafs,
and the outline may be accurately taken, by going over the
piflure with a pencil.
The opake part may be ufed in the day-time without a lamp,
provided the large lenfes at A B are fcreened from the light.
T o use the L ucernal Microscope in the E xamination
OF TRANSPARENT OBJECTS.
The microfcope is to remain as before: the upper part f g s o f
the opake ftage mult be removed, and the ftage for tranfparent
objeCts, reprefented at Fig. 4, put in it’s place; the end, Fig. 9
and 10, to be next the lamp.
Place the greyed glals in it’s groove at the end A B, and the
objefts in the flider-holder at the front o f the ftage ; then tranfmit
as ftrong a light as you are able on the objeCi, which you will
ealily do by railing or lowering the lamp.
The objeCt will be beautifully depicted on the grey glafs : it
mull be regulated to the focus of the magnifier, by turning the
pinion- a.
The objeCt may be viewed either with or without the guide for
the e y e ; a lingle obferver will fee an objeCt to the greatell advantage
by uling this guide, which is to be adjufted as we have
defcribed, page 75. I f two or three wilh to examine the objeCt
- at the fame time, the guide for the eye mult be laid afide.
Take the large lens out o f the groove, and receive the image
on the grey glafs ; in this cafe, the guide for the eye is of.no u fe:
if the grey glafs is taken away, the image , of the objeCt may be
received on a paper fcreen.
Take out the grey glafs, replace the large lenfes, and ufe the
guide for the eye; attend to the foregoing directions, and adjuft
the objeCt to it’s proper focus. You will then fee the object in a
blaze of light almolt too great for the eye, a circumftance that
will be found very ufeful in the examination o f particular objefts ;
the edges of the objeCt in this mode will be fomewhat coloured,
but as it is only ufed in this full light for occafional purpofes, it
has been thought better to leave this fmall imperfection, than by
*$ remedying it, to facrifice greater advantages; the more fo, as this
fault is ealily correfted, and a new and interefting view o f the
objeCt is obtained, by turning the inftrument out of the direCt rays
of light, and permitting them to pafs through only in an oblique
direction, by which the upper furface is in fome degree illuminated,
and the objeCt is feen partly as opake, partly as tranfparent.
It has been already obferved, that the tranfparent objeCts might
be placed between the Aider-holders of the ftage for opake objects,
and then be examined as if opake.