620 
OPT 
IV. Solar Microfeopes. —The folar microfcope was in¬ 
vented, about the year 1738 or 9, by Mr. Lieberkuhn. It 
confifts of a tube, a looking-glafs or mirror, a convex 
Jens, and Wilfon’s Tingle microfcope before defcribed. 
1 he fun’s rays being re fie fled through the tube by means 
of the mirror upon the objedt, the image or pidture of the 
object is thrown diftindtly and beautifully upon a fcreen 
of white paper or a white linen fheet, placed at a proper 
diftance to receive the fame.; and may be magnified to a 
fize not to be conceived by thofe who have not feen it : 
for the farther the fcreen is removed, the larger will 
the objedt appear ; infomuch that a loufe may thus be 
magnified to the length of five or fix feet, or even a great 
deal more; though it is more diftindt when not enlarged 
to above half thgt fize. 
The original conftrudiion is reprefented on Plate XII. 
A, fig. 1. is a fquare wooden frame, through which pafs 
two long fcrews afiifted by a couple of nuts, 1, 1, x. By 
thefe it is faftened firmly to a window-fnutter, wherein a 
hole is made for its reception ; the two nuts being let 
into the flutter, and made fall thereto. The tube C is 
brafs, near two inches in diameter, fixed in a circular 
collar of mahogany, with a groove on its periphery on 
the outfide, denoted by 2, 3, and connected by a cat-gut 
to the pulley 400 the upper part ; which, turning round 
at pleafure, by the largefcrew 5, may be adjufted ealily to 
the hole in the window-fhutter, in fuch a manner that no 
light can pafs into the room but through the aforefaid 
tube C. Faftened to the frame A, by hinges, on the fide 
that goes without the window, is a looking-glafs G, which 
by means of a jointed brafs wire, 6, 7, and the fcrew H8, 
coming through the frame, may be moved either verti¬ 
cally or horizontally, to throw the. fun’s rays through 
the brafs tube into the darkened room. The end of the 
brafs tube without the fnutter has a convex lens 9, to 
coiled! the rays thrown on it by the glafs G, and bring 
them to a focus in the other part, where D is a tube Ai¬ 
ding in and out, to adj lift the objedt to a due diftance from 
the focus; and to the end F of another tube is fcrewed 
one of Wilfon’s Ample pocket-microfcopes, containing 
the object to be magnified in a Aider; and, by the tube F 
Aiding on the fmall end E of the other tube D, it is brought 
to a true focal diftance. 
When this microfcope is employed, the room muft be 
rendered as dark as pofiible ; for, on the darknefs of the 
room, and the brightnefs of the funfhine, depend the 
iljarpnefs and perfedtion of your image. Then putting 
the looking-glafs G through the hole in your window- 
Aiutter, fallen the fquare frame A to the Aiutter by its 
two fcreu's and nuts 1, 1. This done, adjuft your look¬ 
ing-glafs to the elevation and fituation of the fun, by 
means of the jointed wire FI, together with the cat-gut 
and pulley, 3, 4. For, the firft of thefe railing or lowering ' 
the glafs, and the other inclining it to either fide, there 
refulfs a twofold motion, which may eafily be To managed 
as to' bring the glafs to a right pofition, that is, to make 
it refledt the fun’s raysdiredtly through the lens 9, upon 
the paper fcreen, and form thereon a lpot of light exadtly 
round. But, though the obtaining a perfedt circular fpot 
of light upon the fcreen, before you apply the microfcope, 
is a certain proof that your mirror is adjufted right, that 
proof muft not always be expedted : for the fun is To low 
in winter, that, if it fiiine in a direct line againft the -win¬ 
dow, it cannot then afford a fpot of light exactly round ; 
but, if it be on either fide, a round fpot may be obtained, 
even in December. As foon as this appears, fcrew the 
tube D into the brafs collar provided for it in the middle 
of your wood-work, taking care not to alter your looking- 
glafs : then, fcrewing the magnifier you choofe to employ 
to the end of your microfcope in the ufual manner, take 
away the lens at the other end thereof, and place a Aider, 
containing the objedts to be examined, between the thin 
brafs plates, as in the other ways of ufing the microfcope. 
If the light fall not exadtly right, you may eafily, by a 
gentle motion of the jointed wire and pulley, diredt it 
I c s. 
through the axis of the microfcopic lens. The ftiort tube 
F, to which the microfcope is fcrewed, renders it eafy, 
by Aiding it backwards or forwards on the other tube E.,. 
to bring the objedts to their focal diftance ; which will be' 
known by the Aiarpnefs and clearnefs of their appearance : 
they may alfo be turned round by the fame means with¬ 
out being in the leaft difordered. The magnifiers molt 
ufeful in the folar microfcope are, in general, the fourth, 
fifth, or fixth. The fcreen on which the reprefentations 
of the objedts are thrown, is ufually compofed of a fheet' 
of the largeft elephant paper, ftrained on a frame which 
Aides up or down, or turns about at pleafure on a round 
wooden pillar, after the manner of fome fire-fcreens. 
Larger fcreensmay alfo be made of feveral fheets of the 
fame paper pafted together on cloth, and let dqwn from 
the ceiling with a roller like a large map. 
“ This microfcope (fays Mr. Baker) is the moft enter¬ 
taining of'any ; and perhaps the moft capable of making 
difcoverie's in objedts that are not too opaque ; as it fhow$ 
them much larger than can be done any other way. There 
are alfo feveral conveniencies attending it, which no 
other microfcope can have ; for the weakeft eyes may ufe 
it without the leaft draining or fatigue; numbers of peo¬ 
ple together may view any objedf at the fame time ; and, 
by pointing to the particular parts thereof,and difcourfing 
on what lies before them-, may be able better to under- 
ftand one another, and more likely to find out the truth, 
than in other microfeopes, where they muft peep one after 
another, and perhaps fee the objedt neither in the, fame 
light nor in the fame pofition. Thofe alfo, who have no 
lkill in drawing, may, by this, contrivance, eafily (ketch 
out the exabt figure of any objedt they have a mind to 
preferve a pidture of; fince they need only fatten a paper 
on the fcreen, and trace it out thereon, either with a pen 
or pencil, as it appears before them. It is worth the 
while of thofe who are defirous of taking many draughts 
in this way, to get a frame, wherein a fheet of paper may 
be put in or taken out at pleafure; for, if the paper be 
Angle, the image of an objedt will be feen almoltas plainly 
on the back as on the fore fide ; and, by (landing behind 
the fcreen, the (hade of the hand will not obftrudt the 
light in drawing, as it muft in fome degree when one 
(lands before it.” 
. M. Lieberkuhn, however, made confiderable improve¬ 
ments in his folar microfcope, particularly in adapting it 
to the view of opaque objedts; and M. LEpinus (Nov. 
Com. Petrop. vol. ix. p. 326.) contrived, by throwing the 
light upon the fore fide of any objedt, before it is tran'f- 
mitted through the objedt-lens, to reprefent'with equal 
advantage all kinds of objects by it. In this improve¬ 
ment, the body of the common folar microfcope is re¬ 
tained, and only an addition made of two brafs plates, 
C A and B A, fig. 5. joined by a hinge, and kept at a pro¬ 
per diftance by a fcrew. A (edtion of thefe plates, and of 
all the neceffary parts of the inftrument, may be feen in 
fig: 6. where c, «, reprefent rays of the fun con verging from 
the illuminating lens, and falling upon the mirror d b, 
which is fixed to the nearer jiff the byafs plates. From this 
they are thrown upon the object at cf, and thence are 
tranfmitted through the objedt-lens at K, and a perforation 
in the farther plate, upon a fcreen, as ufual. The ufe of 
the fcrew n is to vary the diftance of the two plates, and 
thereby to adjuft the mirror to the objedt with the greateft 
exadtnefs. A v.ery confiderable improvement may be made 
in the folar microfcope, by fubftituting Ramfden’s achro¬ 
matic eye-piece jnflead of the convex objedt-lens. 
An improved folar microfcope, as nfed with the ftvgle mi- 
crofcope , with teeth and pinions, is fhown at figs. 7 and 8. 
Fig. 7' reprefen ts the whole form of the fugle microfcope; 
the parts of whicff.are as follows : ABCD, the external 
tube; GHIK, the internal, movable one; QM, part of 
another tube within the lafl, at one end of which is fixed a 
plate of brafs hollowed in the middle, for receiving the 
glafs tubes: there is alfo a movable flat plate, between 
which and the fixed end of the fecond tube the ivory 
fli ders 
