G22 OPT 
Proper form. The facility with which all opaque objects 
are applied to this inltrument, is another confiderable 
advantage, and almoft peculiar to itfelf: as the texture 
and configuration of the more tender parts are often hurt 
by previous preparation, every objeft may be examined by 
this inftrument, firft as opaque, and afterwards (if the 
texture will admit of it) as tranfparent. The lucernal 
rnicrofcope does notin the leaft fatigue the eye ; the ob¬ 
ject appears like nature itfelf, giving eafe to the fight and 
pieafure to the mind : there is alfo, in the life of this in¬ 
ftrument, nooccafion to fhut the eye which is not direfted 
to the objeft. A further advantage peculiar to this.mi- 
crofcope is, that by it the outlines of every objeft may be 
taken, even by thofe who are not accultomed to draw; 
while thofe who can draw well will receive great aflift- 
ance, and execute their work with more accuracy and in 
lefs time than they would otherwife have been able to have 
performed it. Tranfparent objects as well as opaque may 
be copied in the fame manner. The inftrument may be 
uled at anytime of the day, but the belt effeft is by night; 
in which refpeft it has a l'uperiority over the folar micro- 
fcope, as that inftrument can only be ufed when the fun 
fhinesj 
Tranfparent objefts may be examined with the lucernal 
rnicrofcope in three or four different modes, from a blaze 
of light almoft too great for the eye to bear, to that which 
is perfedlly eafy to it: and, by the addition of a tin lan¬ 
tern to the apparatus, may be thrown on a fcreen, and 
exhibited at one view to a large company, as by the folar 
rnicrofcope. 
We ( 1 :all now proceed to the defcription of the inftru- 
ment and apparatus, as given by Mr. Adams. Fig. 9. 
reprefents the improved lucernal rnicrofcope, mounted to 
view opaque objedts. ABCD is a large mahogany py¬ 
ramidal box, which forms the body of the rnicrofcope ; it 
is fupported firmly on the brafs pillar FG, by means of 
the focket H and the curved piece IK. LMN is a guide 
for the eye, in order to direft it in the axis of the lenfes ; 
it confifts of two brafs tubes, one Hiding wdthin the other, 
and a vertical flat piece, at the top of which is the hole for 
the eye. The outer tube is feen at MN, the vertical piece 
is reprefented at LM. The inner tube may be pulled out, 
or pufbed in, to adjuft it to the focus of the glaffes. The 
vertical piece may be raifed or depreffed, that the hole, 
through which the objeft is to be viewed, may coincide 
with the centre of the field of view ; it is fixed by a milled 
lcrew at M, wdiich could not be fhown in this figure. At 
N is a dove-tailed piece of brafs, made to receive the dove¬ 
tail at the end of the tubes MN, by which it is affixed to 
the w'ooden box ABCDE. The tubes MN may be re¬ 
moved from this box occafionally, for the convenience of 
packing it up in a lefs compafs. OP, a fmall tube which 
carries the magnifiers. O, one of the magnifiers; it is 
fcrewed into the end of a tube, which Aides within the 
tube P ; the tube P may be unfcrewed occafionally from 
the wooden body. QRSTVX is a long fquare bar, wdiich 
pafles through the fockets YZ, and carries the ftage or 
frame that holds the objefts; this bar may be moved 
backward or forward, in order to adjuft it to the focus by 
means of the pinion which is at a. b, A handle furniflied 
with an uni verbal-joint, for more conveniently turning 
the pinion. When the handle is removed, the nut, s, may 
be ufed in its Head, cle, A brafs bar, to fupport the curved 
piece KI, and keep the body AB firm and fteady. fg'hi, 
The ftage for opaque objefts: it fits upon, the bar QRST 
by means of the focket hi, and is brought nearer to, or 
removed farther from, the magnifying lens, by turning the 
pinion a: the objefts are placed in the front fide of the 
ftage (which cannot be feen in this figure) between four 
fmall brafs plates; the edges of two of tliefe are feen at 
Id. The two upper pieces of brafs are movable; ^they 
are fixed to a plate, which is afted on’ by a fpiral ip ring, 
that prefles them down, and confines the Aider with the 
objedls : this plate, and the two upper pieces of brafs, are 
lifted up by the fmall nut m. At the lower part of the 
ICS. 
ftage, there is a femicircular lump of glafs, n, which is de. 
figned to receivejjthe light from the lamp, and t 
and throw it on the concave mirror c, whence it is to 
be reflefted on the objeft. The upper part,^ 7 ij, of the 
opaque ftage, takes out, that the ftage for transparent ob¬ 
jefts may be inferted in its place. 
Fig. 10. reprefents the ftage for tranfparent objedls ; the 
two legs 5 and 6 fit into the top of the under part rshi of 
the ftage for opaque objedts; 7 is the part which confines 
or holds the Aiders, and through which they are to be 
moved ; 9 and to, a brafs tube, which contains the lenfes 
for condenling the light, and throwing it upon the objedt; 
there is a fecond tube, within that marked 9 and 10, which 
may be placed at different diftances from the objedt by the 
pin 11. When this ftage is ufed as a fingle rnicrofcope, 
without any reference to the lucernal, the magnifiers, or 
objedt-lenfes, are to be fcrewed into the hole 12, and to be 
adjufted to a proper focus by the nut 13. 
At the end AB, fig. 9, of the wooden body, there is a 
Aider, which is reprefented as partly drawn out at A : 
when quite taken out, three grooves will be perceived ; 
one of which contains a board that forms the end of the 
box ; the next contains a frame with a greyed glafs ; and 
the third, or that fartheft from the end AB, two large 
convex lenfes. 
In the ufe of this rnicrofcope for examining opaque 
objects, take out the wooden Aider A, and lift out the 
cover and the grey glafs from their refpedtive grooves 
under the Aider A. Put the end N of the guide for the 
eye LMN into its place, fo that it may Hand in the pofition 
which is reprefented in this figure. Place the focket, 
which is at the bottom of the opaque ftage, on the bar 
QXT, fo that the concave mirror o may be next the end 
DE of the wooden body. Screw the tubes P, O, into the 
end DE. The magnifier you intend to ufe is to be fcrewed 
on the end O of thefe tubes. The handle b, or the milled 
nut c, mull be placed on the fquare end of the pinion a. 
Place the lamp lighted before the glafs lump n, and the 
objeft you intend to examine between the fpring-plates of 
the ftage ; and the inftrument is ready for ufe. 
In all microfcopes there are two circumftances which 
mull be particularly attended to: Firft, the modification 
of the light, or the proper quantity to illuminate the ob¬ 
jeft; fecondly, the adjuftment of the inftrument to the 
focus of the glafles and eye of the obferver. In the ufe of 
the lucernal rnicrofcope there is a third circumftance; 
which is, the regulation of the guide for the eye. 
1. To throw the light upon the objeft: The flame of 
the lamp is to be placed rather below the centre of the 
glafs lump n, and as near it as pofiible ; the concave mirror 
O mull be fo inclined and turned as to receive the light 
from the glafs lump, and refleft it thence upon the objedt .- 
the belt fituation of the concave mirror and the flame of 
the lamp depends on a combination of circumftances, 
which a little praftice will difcover. 
2. To regulate the guide for the eye, or to place the 
centre of the eye-piece L fo that it may coincide with the 
focal point of the lenfes and the axis of vifion : Lengthen 
and fliorten the tubes M, N, by drawing out or pufliing in 
the inner tube, and railing or deprefling the eye-piece ML, 
till you find the large lens (which is placed at the end AB 
of the wooden body) filled by an uniform field of light, 
without any prifmatic colours round the edge ; for, till this 
piece is properly fixed, the circle of light will be very 
imall, and only occupy a part of the lens : the eye mull 
be kept at the centre of the eye-piece L during the whole 
of the operation ; which may be rendered fomewhat eafier 
to the obferver, on the firft ufe of the inftrument, if he 
hold a piece of white paper parallel to the large lens, re¬ 
moving it from, or bringing it nearer to, them, till he find 
the place where a lucid circle, which he will perceive on 
the paper, is brighteft and mod diftinft ; then he isdo fix 
the centre of the eye-piece to coincide with that fpot; 
after which a very fmall adjuftment will fet it perfeftly 
right. 
3. To 
