£J2 OPT 
Tlie ingenious Mr. Grey hit upon a very eafy expedient 
to make very good temporary microfcopes, at a very little 
-expenfe. They confift cf nothing bat fmall drops of wa¬ 
ter, takenn up with a point of a pin, and put into a fmall 
hole made in a piece' of metal. Thefe globules of water 
tdo iiot, indeed, magnify lo much as thole which are made 
of glafs of the fame fize, becaufe the refractive power of 
water is not fo great; but the fame purpofe will be an- 
fwered nearly as well by making them fomewhat fmaller. 
The fame ingenious perfon, obferving that fmall hetero¬ 
geneous particles inclofed in the glafs of which micro¬ 
fcopes are made, were much magnified when thole glafles 
were looked through, thought of making his microfcopes 
of water that contained living animalcula, to fee how 
they would look in this new lituation ; and he found his 
fcbeme to anfwerbeyond his expectation, fo that he could 
not even account for their being magnified fo much as 
they were; for it was much more than they would have 
been magnified if they had been placed beyond the glo¬ 
bule, in the proper place for viewing objects. But Mon- 
tucla obferves, that, when any objeft is inclofed within 
this fmall tranfparent globule, the hinder-part of it aCts 
like a concave mirror, provided they be fituated between 
that furface and the focus ; and that, by this means, they 
are magnified above 3! times more than they would have 
been in the ufual way. 
Temporary microfcopes of a different kind have been 
conftruCted by Dr. Brewfter. They were compofed of tur- 
-pentine-varnifii, which was formed into a plano-convex 
lens, by laying a drop of it upon a piece of plain glafs: 
the under furface of the glafs was then fmoked, and the 
black pigment removed immediately below the fluid lens. 
Thefe lenfes lafted for a long time, and fliowed objects 
diftinCtly, even when combined into a compound micro- 
flcope. See the Appendix to Fergufon’s LeCtures, vol. ii. 
After the fuccefsful conltruCtion of the reflecting tele- 
fcope, it was natural to expeft that attempts would alfo 
be made to render a fimilar fervice to microfcopes. Ac¬ 
cordingly we find two plans of this kind. The firft was 
that of Dr. Robert Barker. His inftrument differs in no¬ 
thing from the reflecting telefcope, excepting the diltance 
of the fwo fpeculums, in order.to adapt it to thole pen¬ 
cils of rays which.enter the microfcope diverging; whereas 
they come to the telefcope from very diftant objects nearly 
parallel to each other. But this microfcope is not fo ealy 
to manage as thofe of the common kind. For vifion by 
reflection, as it is much more perfect, fo it is far more diffi¬ 
cult, than that by refradtion. Nor is this microfcope fo 
clef ill for any but very fmall or tranfparent objedts. For 
the objedt, being between the fpeculum and image, would, 
if it were large and opaque, prevent a due reflection. 
Dr. Smith invented a double reflecting microfcope, of 
which a theoretical and practical account is given, in his 
remarks at the end of the fecond volume of his Syftem of 
Optics. 
M. Lieberkuhn, in 1738 or 1739, tnade two capital im¬ 
provements in microfcopes, by the invention of th t folar' 
■microfcope> and the microfcope for opaque objects. When 
lie was in England, in the winter of 1739, he fliowed an 
apparatus for each of thefe purpofes, made by himfelf, to 
.feveral gentlemen of the Royal Society, as well as to 
•feme opticians. The microfcope for opaque objedts re¬ 
medies the inconvenience of having the dark fide of an 
objedt next the eye. For, by means of a concave fpecu- 
lum of filver, highly poliflied, in the centre of which a 
magnifying lens is placed, the objedt is lo ftrongly illumi¬ 
nated, "that it may be examined with all imaginable eafe 
.and pieafure. A convenient apparatus of this kind, with 
four different fpecula and magnifiers of different powers, 
was brought to perfection by Mr. Cuff in Fleet-ftreet. 
M. Lieberkuhn made conffderable improvements in his 
.folar microfcope, particularly in adapting it to the view 
of opaque objedts ; but in what manner this was effected, 
.M.aEpinus, who-was highly entertained with the per¬ 
formance, and who mentions the fadt, was not able to 
I c s. 
recollect; and the death of the ingenious inventor pre¬ 
vented his publifhingany account of it himfelf. ZEpinus 
invites thole who came into the pofl’eflion of Lieberkuhn’a 
apparatus, to publifh an account of this inftrument; but 
it does not appear that his method was ever publifhed. 
This improvement of M. Lieberkuhn’s induced M. 
^Epinus himfelf to attend to the fubjedt; and he thus pro¬ 
duced a very valuable improvement in this inftrument. 
For, by throwing the light upon the fore-fideof any objedt 
by means of a mirror, before it is tranfmitted through the 
objedt-lens, all kinds of objedts are equally well repre- 
fented by it. 
Several improvements were made in the apparatus to the 
folar microfcope, as adapted to view opaque objedts, by M. 
Zeiher, who made one conftrudtion for the larger kind of 
objedts, and another for the fmall ones. 
The conftrudtion of a telefcope with fix eye-glafles 
led M. Euler to a fimilar conftrudtion of microfcopes, by 
introducing into them fix lenfes, one of which admits 
of fo fmall an aperture as to ferve, inftead of a dia¬ 
phragm, to exclude all foreign light; though, as he fays, 
it neither leflens the field of view nor the brightnefs of 
objedts. 7 
As for the methods of calling little glafs fpherules for 
microfcopes, they are various. The firft perfon who im¬ 
proved Angle microfcopes by ufing fmall globules of glafs, 
made by melting them in the flame of a candle, was 
Hartfocker, who thus difeovered the animalcula in feinine 
mafqulino, and laid the foundation of a new fyftem of 
generation. Wolfius deferibes the following method of 
making globules of this kind : A fmall piece of very fine 
glafs, flicking to the wet point of a fleet needle, is to be 
applied to the extreme bluifh part of the flame of a lamp, 
or, which is better, to the flame of fpirit of wine, to pre¬ 
vent its being blackened : being there melted and run 
into a little round drop, it is to be removed from the flame, 
upon which it inftantly ceafes to be fluid ; folding, then, 
a thin plate of brafs, and making very fmall fmooth per¬ 
forations, loasnot to leave any roughnefs on thefurfaces; 
and farther, fmooth them over, to prevent any glaring, fit 
the fpherule between theplates, againit the apertures, and 
put the whole in a frame, with objedts convenient for ob- 
iervation, 
Mr. Adams gives another method, thus : Take a piece 
of fine window-glafs, and raife it, witji a diamond, into 
as many lengths as you think needful, not exceeding an 
eighth of an inch in breadth ; then, holding one of thofe 
lengths between the fore-finger and the thumb of each 
hand, over a very fine flame, till the glafs begins to fof- 
ten, draw it out till it be as fine as a hair, and break ; 
then, applying each of the ends into the pureft part of 
the flame, you have two fpheres prefently, which you 
may make larger, or lefs, at pieafure: if they ftay long in 
the flame, they will have (pots; fo they mult be drawn out 
immediately after they are turned round. As to the Item, 
break it off as near the ball as poffible ; and, lodging the 
remainder of the Item between theplates, by drilling the 
hole exadtly round, all the protuberances are buried be¬ 
tween the plates, and the microfcope performs to admi¬ 
ration. 
Mr. Butterfield, in the Phil. Tranf. N° 141, recom¬ 
mends, for making glafs globules clear and without 
fpecks, the flame of a lamp made with rectified Ipirit of 
wine, and, inftead of a cotton wick, fine Alver-wire, dou¬ 
bled like a Ikain of thread ; then having beaten fome fine 
glafs to powder, and walhed it clean, he directs to take 
a little of it upon the lharp point of a filver needle, wet¬ 
ted with fpittle, and to hold it in the flame, turning it 
about till it melts, and becomes quite round. When 
many globules are thus formed, he rubs them with loft 
leather; and, having feveral fmall pieces of thin brafs 
plates, twice as long as they are broad, he doubles them 
up into the form of a lquare, and pulhes a fine hole through 
the middle of them, and having rubbed off' the bur about 
the holes with a whetftone, and blackeued the iufide of 
the 
