OPT 
drawer or cafe, fo as to ftand perfectly firm and fteady. 
C is a brafs fcrew, that pafl'es through a hole in the upper 
limb of the fcroll into the fide of the microfcope D, and 
fcrews it faft to the faid fcroll. Elsa concave fpeculum 
fet in a box of brafs, which hangs in the arch G by two 
final 1 fcrews ff, that fcrew into the oppofite fides thereof. 
At the bottom of this arch is a pin of the fame metal, ex¬ 
actly fitted to a hole h in the wooden pedeftal. As the 
arch turns on this pin, and the fpeculum turns on the 
end of the arch, it may, by this twofold motion, be ea- 
fily adjlifted in fuch a manner as to reflect the light of the 
fun, of the Iky, or of a candle, directly upwards through 
the microfcope, that is fixed perpendicularly over it; and 
by fo doing may be made to anfwer many purpofes of the 
large double reflecting microfcope. The body of the mi¬ 
crofcope may alfo be fixed horizontally, and objefts viewed 
in that pofition by any light you choofe; which is an ad¬ 
vantage the common double reflecting microfcope has not. 
It may alfo be rendered further ufeful by means of a flip of 
glafs ; one end of which being thruft through between the 
plates where the Aiders go, and the other extending to fome 
diftance, fuch objefts may be placed thereon as cannot 
be applied in the Aiders; and then, having a limb of brafs 
that may fatten to the body of the microfcope, and ex¬ 
tend over the projecting glafs a hollow ring wherein to 
fcrew the magnifiers, all forts of fubjeCts may be examined 
with great convenience, if a hole be made in the pedeftal, 
to place the fpeculum exaftly underneath, and thereby 
throw up the rays of light. The pocket-microfcope, 
thus mounted, fays Mr. Baker, “ is as eafy and pleafant 
in its ufe as fit for the moll curious examination of the 
animalcules and falts in fluids, of the farinas in vegeta¬ 
bles, and of the circulation in fmall animals 5 in fliort, it is 
as likely to make confiderable difcoveries in objefts that 
have fome degree of tranfparency, as any microfcope I 
have ever feen or heard of.” The brafs fcroll A is now ge¬ 
nerally made to unfcrew into three parts,and pack with the 
microfcope and apparatus into the drawer of a mahogany 
pocket-cafe, upon the lid of which the fcroll is made to 
fix when in ufe. 
Gray’s water-microfcope is reprefented at fig. 8. The 
drop of water taken up on the point of a pin is intro¬ 
duced into the fmall hole D, of an inch in diameter, 
in the piece of brafs DE, about of an inch thick. The 
hole D is in the middle of a fpiierical cavity, about $ of 
an inch in diameter, and a little deeper than half the 
thicknefs of the brafs; on the oppofite fide cf the brafs is 
another fpiierical cavity, half as broad as the former, and 
fo deep as to reduce the circumference of the fmall hole 
to a (harp edge. The water, being placed in thefe cavities, 
will form a double convex lens with unequal convexities. 
The objeft, if it is folid, is fixed upon the point C of the 
fupporter AB, and placed at its proper diftance from the 
water-lens by the fcrew FG. When the objeft: is fluid, it 
is placed in the hole A, but in fuch a manner as not to 
Ire fpiierical 5 and this hole is brought oppofite the fluid 
lens bv moving the extremity G of the fcrew into the flit 
GH. 
Ellis’s aquatic microfcope has the advantage of being 
Ample in its confirmation, portable, and very commodious 
for the purpofes of practical botanifts, the obfervers of ani- 
malcula, &c. K, fig. 9, reprefents the box containing 
the whole apparatus : it is generally made of fifli-fkin 5 
and at K there is a female fcrew, for receiving the fcrew 
that is at the bottom of the pillar A : this is a pillar of 
hrafs, and is fere wed on the top of the box. D is a brafs 
pin which fits into a hole bored through the middle of the 
pillar. On the top of this pin is a hollow focket to re¬ 
ceive the arm which carries the magnifiers; the pin is to 
be moved up and down, in order to adjuft the lenfes to 
their focal or proper diftance from the objeft. E, the bar 
which carries the magnifying lens; it fits into the fccket 
X, which is at the top of the pin or pillar D. This arm 
may be moved backwards and forwards in the focket X, 
and Tideways by the pin D 5 fo that the magnifier, which 
ICS. 615 
is ferewed into the ring at the end E of this bar, may he 
eafily made to traverfe over any part of the object that 
lies on the ftage or plate B. FF is a polifhed filver fpe¬ 
culum, with a magnifying lens placed at the centre thereof, 
which is perforated for this purpofe. The filver fpeculum 
fcrews into the arm E, as at F. Other fpecula, with their 
lenfes, of different magnifying powers, may be provided 
to fix on occafionally. H is the femicircle which fupports 
the mirror I; the pin R, affixed to the femicircle H, pafl'es 
through the hole which is towards the bottom of the pil¬ 
lar. A. B is the ftage, or the plane, on which the objefts 
are to be placed ; it fits into the fmall dove-tailed arm at 
the upper end of the pillar DA. A plane round glafs, 
with a fmall piece of black filk ftuck on it, is 11 fed to lie 
in a circular groove made in the ftage B. A hollow 
watch-glafs is to be laid occafionally on the ftage inftead 
of the plane glafs. A pair of nippers, L, fig. 10, is 
fixed to the ftage by the pin K at bottom; the fteel wire 
of thefe nippers Aides backwards and forwards in the foc¬ 
ket, and this focket is movable upwards and downwards 
by means of the joint, fo that the pofition of the object 
may be varied at pleafure. The objeft maybe fixed in the 
nippers, ftuck on the point, or fixed by a little gum- 
water, &c. to the ivory cylinder. N, which occafionally 
fcrews to the point of the nippers 
To ufe this microfcope: Take all the parts of the appa¬ 
ratus out of the box; then begin by ferewing the pillar 
A to the cover of it; pafs the pin R of the femicircle 
which carries the mirror through the hole that is near the 
bottom of the pillar A; pufti the ftage into the dove-tail 
at B, Aide the pin into the pillar; then pafs the bar E 
through the focket which is at the top of the pin D, and 
fcrew one of the magnifying lenfes into the ring at F. 
The microfcope is now ready for ufe; and, though the 
enumeration of the articles may lead -the reader to ima¬ 
gine the inftrument to he of a complex nature, we can 
fafely affirm that he will find it otherwife. The inftru¬ 
ment has this peculiar advantage, that it is difficult to put 
any of the pieces in a place which is appropriated to an¬ 
other. Let the objeft be now placed either on the glafies 
of the ftage, or in the nippers L, and in fuch manner that 
it may be as nearly as poflible over the centre of the ftage ; 
bring the fpecula F over the part you mean to obferve • 
then throw as much light on the fpeculum as you can, 
by means of the mirror I, and the double motion of 
which it is capable; the light received on the fpeculum 
is reflefted by it on the objeft. The diftance of the 
lens F from the objeft is regulated by moving the pin 
D up and down, until a diftinct view of it is obtained. 
The beft rule is, to place the lens beyond its focal dif¬ 
tance from the objeft, and then gradually to Aide it down 
till the objeft appears (harp and well defined. The ad- 
juftment of the lenfes to their focus, and the diftribution 
of the light on the objeft, are what require the greateft 
attention: on the firft the diftinftnefs of the vifion de¬ 
pends; the pleafure arifing from a clear view of the parts 
under obfervation is due to the modification of the lio-ht. 
No precife rule can be given for attaining accurately thefe 
points ; it is from practice alone that ready habits cf ob¬ 
taining thefe neceflary properties can be acquired, and 
with the afiiftance of this no difficulty will be found. 
Mr. Benjamin Martin alfo contrived a microfcope for 
fimilar purpofes with tbofe to which that of Mr. Ellis is 
adapted. AB, fig. 11, reprefents a fmall arm fupportino- 
two or more magnifiers, one fixed to the upper part as at 
B, the other to the lower part of the arm at C; thefe may¬ 
be ufed feparately or combined together. The arm AB is 
fupported by the fquare pillar IK, the lower end of which 
fits into the focket E of the foot FG; the ftage DL is 
made to Aide up and down the fquare pillar; H, a concave 
mirror for reflecting light on the objeft. To ufe this mi¬ 
crofcope, place the objeft on the ftage, refleft the light on 
it from the concave mirror, and regulate it to the focus 
by moving the ftage nearer to or farther from the lens at 
B. The ivory Aiders pafs through the ftage; other ob¬ 
jects 
