GI7 
OPTICS. 
which is alfo a very great advantage, the axis of the mi- 
crofcope is always kept perpendicular to that point of the 
cibjeft over which it was firft placed; fo that here is not 
the inconvenience which occurs in other glafles, of often 
Iofing the light of the object,'by (brewing the glafs C 
higher or lower. PQ is a glafs objeft-plate fixed in a brafs 
frame, whofe arm NN is fixed to the pillar by means of 
the nut O. The arm NN hath in it a (lit, by which it is 
eafily put on or taken off the pillar, and by which it may 
be fixed upon it at any diftance. P, a fmall fifii lying on 
the glafs-plate, that the circulation of the blood may be 
feen in the end of the tail-fin. It, a convex glafs, by 
\yhofe help a bright fp'ot of light is brought from a can¬ 
dle at S, (landing on the ground, while the microfcope 
Hands on the edge of a table or (tool, which fpot of light, 
c, ferves to render the circulation more confpicuous. V, 
a leaden coffin to be put on the fiffi, to hinder it from 
fpringing away, or moving its tail out of the light: but 
a more convenient apparatus for confining a live fiffi will 
be defcribed farther on. The figures i, 2, 3, 4, 5, 6, are 
marked on the pillar LK, to fliow the refpefttive diltances 
of the objeft-glafles from the objeft you look upon, ac¬ 
cording as the objeft-glafles you make ufe of magnify 
more orlefs. Thus, for inftance, if you ufe the objeft- 
glafs 5 or 6, (either of which will (how the circulation of 
the blood,) you mult fix the upper edge of the collar E 
at the,mark 5 or 6 on the pillar : and then the microfcope 
will be very near its exact diftance from the object; fo 
that, by a fmall turn or two of the nut I one way or the 
other, to be found by trial, you may foon fit it exaftly 
to your own eye. By this microfcope liquors alio may be 
very commodioufly examined ; for, if you place a fmall 
drop of any liquor on the glafs-plate, juft: in the middle 
of the fpot of light c, the parts of it will become very 
vifible, and its animalcula, if it have any, will be difco- 
vered. And thus may the eels in vinegar, the fmall 
creatures in black-pepper w^ter, or in water where wheat, 
barley, &c. has been infufed, or the eels and other fmall 
living creatures in puddle-water, be as plainly feen as by 
almolt any other microfcope. 
Culpeper's microfcope, contrived by him and Mr. Scar¬ 
lett, is an improvement of Mr. Marlhal’s. This is repre- 
fented at fig. 2. by which it will be feen that the objects 
are illuminated by reflection. The inner tube AB, which 
Aides in the outer, CD, holds all the glafles. Tlie.eye- 
glafs is at AA, the broad middle glafs at BB, and the op- 
jeft-glafs, being fet in a button at e, is fcrewed upon the 
end of a narrower tube FG; which, being fixed in the 
bafe of the inner tube, pafles freely through a hole in the 
bafe of the outer. The buttons, that contain, feveral ob- 
jeft-gl'afles, are marked j, 2, 3, &c. and the convexity of 
the inner tube is alfo marked with dotted circles, num¬ 
bered 1, 2, 3, &c, in order to bring that circle to coincide 
with the mouth CC of the outer tube, whofe number is 
the fame as that of the objeft-glafs then made ufe of. 
But, if the object does not yet appear quite diftinft, the 
pinion R mnft be turned, which, by a rack on the tube of 
the microfcope, brings it nearer to the objeffi placed below 
it. Of thefe glafles the greater magnifiers are known by 
their having fmaller apertures. The bafe DD of the outer 
tube is fupported by three brafs pillars, fixed into a wooden 
pedeftal FI ; and a little below the objeft-glafs F, a cir¬ 
cular plate IK,is fixed like a ftage between the pillars, 
having a circular hole in the centre to receive glafles, &c. 
to place objects upon. Three fmall brafs circles mu, with 
holes through the middle of them, are to be'placed over 
the hole in the middle of the ftage; and then the ivory 
Aiders with objects may be put between the - two upper- 
mod: of thefe circles, which are prefied together byafpiral 
fpringing wire lodged between the two undermoft; the 
two outermed being held together by two fmall pillars 
pafllng through two holes in the circumference of the 
middle circle. For viewing tfte circulation of the blood, 
the button p, on the under fide of the frame of abroad 
‘plane glafs qr, being put through a flit made in the ftage, 
Vot. XVII. No. 1202. 
a fmall brafs bolt S, under the ftage, muft be fhoved in¬ 
wards, till a fmaller flit in it embraces the neck of the 
faid button; and then the fifti being laid upon this glafs, 
and the body of it covered with the leaden coffin V, fig. 1. 
its tail may be brought exactly under the objeft-glafs by 
turning the glafs pq about the button, or by (hoving it in¬ 
wards or outwards along the flit in the ftage. The cir¬ 
cular objeft-plate vx has a like button in the centre, to be 
put into the fame flit as before ; and then the different 
objefts, placed between two talcs in the holes made round 
the circumference of the plate, may be viewed fucceffively 
by turning the plate about its centre. 
.Ail thele tranfparent objefts are illuminated extremely 
well in this microfcope, either by candle-light or iky-light, 
reflefted upwards from a concave looking-glafs YZ, placed 
in a frame from the centre H of the pedeftal. While you 
are viewing the objeft through the microfcope, turn this 
concave upon its horizontal poles YZ, and you will foon 
find out that pofition of it in which it reflefts the mall 
light through the hole in the ftage upon the objeft ; and 
this happens when it reflefts the rays very obliquely. 
Opaque objefts, when laid upon a black ebony or a white 
ivory plate, put into the hole upon the ftage, may be illu¬ 
minated by candle-light tranfmitted through a double 
convex lens a, b,c-, the (lent of the frame c, in which it 
turns, being put into the.hole in the ftage. The candle 
muft be placed in a line drawn from the objeft through 
the middle of this lens, at fuch a diftance from it as (hall 
caufe the fpot of light upon the objeft-plate to be the 
narrowed:. By day-light this lens gives little or no ad¬ 
vantage to the direft (ley-light. 
Mr. Adams, in his Eflays, has defcribed an improvement 
of this kind of microfcope, which is as follows : AB, fig. 3. 
reprefents the body of the microfcope, containing a double 
eye-glafs and a body-glafs : it is here ffiown as fcrewed to 
the'arm CD, from whence it may be occafionally removed, 
either for the convenience of packing, or when the inftru- 
riient is to be ufed as a (ingle microfcope. The eye-glafles 
and the body-glafles are contained in a tube which fits 
into the exterior tube AB; by pulling out a little this 
tube when the microfcope is in ufe, the magnifying power 
of each lens is increafed. 
The body AB of the microfcope is fupported by the arm 
CD; this arm is fixed to the main pillar CF, which -is 
fcrewed firmly to the mahogany pedeftal GH; there is 
fometimes a drawer to this pedeftal, which holds the ap¬ 
paratus. NIS, the plate or ftage which carries the flider- 
holder KL : this ftage is moved up or down the pillar CF, 
by turning the milled nut M ; this nut is fixed to a pinion, 
that works in a toothed rack cut on one fide of the pillar. 
By means of this pinion, the ftage may be gradually railed 
or deprefied, and the objeft adjufted to the focus of the 
different lenfes. KL is a Aider-holder, which fits into a 
hole that is in the middle ftage NIS; it is ufed to confine 
and guide either the motion of the Aiders which contain 
the objefts, or the glafs tubes that are defigned to confine 
fmall fillies for viewing the circulation of the blood. The 
Aiders are to be pafled between the two upper plates, the 
tubes through the bent plates. L is a brafs tube, to the 
lower part of which is fixed the condenfing lens for con¬ 
centrating the light reflefted up from the mirror O ; it fits 
into the under part of the Aider-holder KL, and may be 
fet at different diftances from the object, according to its 
diftance from the mirror or the candle. O is the frame 
which holds the two reflefting. mirrors, one of which is 
plane, the other concave. Thefe mirrors may be moved 
in various direftions, in order to refleft the light properly, 
by means of the pivots on which-they move in the femi- 
circle QSR, and the motion of the femicircle itfelf on the 
pin S: the concave mirror generally anfwers belt in the 
day-time; the plane mirror combines better with the con¬ 
denfing len-s, and a lamp or candle. At D there is a focket 
for receiving the pin of the arm Q, fig. 4, to which the 
‘concave fpeculum R, for reflefting light on opaque ob¬ 
jefts, is fcrewed. At S is a hole and flit for receiving 
7 S either 
