OPT 
telefcopes will not perform. Quiet ferene nights, when 
there is no moon, are the mod favourable. When com¬ 
paring telefcopes, we fliould take very particular care that 
the eye-tubes be glaffed with the fame fort of glafs, and 
that they a're charged with precifely the fame magnifying 
powers 5 otherwife the companion will be in vain: a dif-*- 
ference of even five or ten times in the magnifying power 
will fometimes, on feme objects, give a different charac¬ 
ter to the glafs ; and, whatever difference there may be in 
the fize of the inftruments, when we wifh to become ac¬ 
quainted with their refpective advantages, they fhould 
each be charged with the fame magnifying power, which, 
if the telefcopes are intended for aftronomical ufe, fhould 
not be lefs than ioo times ; if for terreftrial purpofes, not 
lefs than 50 times. Kitchener's P radical Observations on 
Telefcopes , 1815. Monthly Mag. for Nov. 1816. 
Monf. Galland the geometrician, of Charveaux, near 
Niort, in the department of the Two Sevres, has lately 
obtained from the French government a brevet of inven¬ 
tion for a new fyftem of optics and heliphlogia. This 
learned man fupplies the place of concave and convex 
glaffes by dioptric fquares, which magnify or approximate 
objects, by reprefenting their images in a uniform manner 
011 all the points of their furfaces, which is not done by 
the ordinary glaffes. His quadrangular diophlogia pre¬ 
fen ts a very great and very valuable economy of combuf- 
tible fubftances, by uniting in one point a great number 
of burning foci, which produce, at pleafure, all the de¬ 
grees of heat necefiary for the ufage^ of life, and the 
fciences and arts. 
Microscopes. Plate X. XI. XII. 
The invention of microfcopes was not much later than 
that of telefcopes ; and, according to Borellus, we are 
indebted for them to the fame perfon, at leaf!: to Zacharias 
Janfen, in conjunction wifh his fon. The Janfens, how¬ 
ever, have not always enjoyed, undifturbed, that fliare of 
reputation to which they feem tb be entitled, with refpeft: 
either to the telefcope or the microfcope. The difcovery 
of the latter, in particular, has generally been confidered 
as more uncertain than that of the former. All that 
many writers fay we can depend upon is, that microfcopes 
were fir ft ufed in Germany about the year 1621. Others 
fay pofitively, that this instrument was the contrivance of 
Cornelius Drebell, a man of ingenuity, who alfo invented 
the thermometer. See p. 545. 
According to Borellus, Zacharias Janfen and his fon 
prefented the firft microfcopes they had conftrufted to 
prince Maurice, and Albert archduke of Auftria. Wil¬ 
liam Borell, who gives this account in a letter to his bro¬ 
ther Peter, fays, that, when he was ambafladorin England, 
in 1619, Cornelius Drebell, with whom he was intimately 
acquainted, fhowed him a microfcope, which he faid was 
the fame which the archduke had given him, and had 
been made by Janfen himfelf. This inftrument was not 
fo fhort as they are generally made at prefent, but was fix 
feet long, confiding of a tube of gilt copper, an inch in 
diameter, fupported by three brafs pillars in the fliape of 
dolphins, on a bafe of ebony, on which the fmall objects 
were placed. This microfcope was evidently a compound 
one, or rather fomething betwixt a telefcope and a mi¬ 
crofcope; fo that it is poflible, that fingle microfcopes 
might have been known, and in ufe, fame time before; 
but perhaps nobody thought of giving that name to fin¬ 
gle lenfes ; though, from the firft ufe of lenfes, they could 
not but have been ufed for the purpofe of magnifying 
fmall objects. In this fenfe we have feen, that even the 
ancients were in pofiefiion of microfcopes ; and it appears 
from Jamblicus and Plutarch, quoted by Dr. Rogers, 
that they gave fuch inftruments as they ufed for this pur¬ 
pofe the name of dioptra. At what time lenfes were made 
fo fmall as we now generally ufe them for magnifying in 
fingle microfcopes, we have not found. But, as this mull 
necefiarily have been done gradually, the only proper ob¬ 
ject of inquiry is, the invention of the double or compound 
ICS. > 6*11 
microfcope; and this is clearly given, by the evidence of 
Borellus above mentioned, to Zjacharias Janfen, his fon. 
The invention of compound microfcopes is claimed by 
the fame Fontana who arrogated to himfelf the difcovery 
of telefcopes j and, though he did not publifh any account 
of this invention till the year 1646, (notwithftanding he 
pretended to have made the difcovery in 1618,) Montucla, 
not from attending perhaps to the teltimony of Borellus, 
is -willing to allow his claim, as he thought there was no 
other perfon who feemed to have any better title ro it. 
Euftachio Divini made microfcopes with two common 
objeft-glafies, and two plano-convex eye-glades joined 
together on their convex fides lo as to meet in a point. 
The tube in which they were inclofed was very large, and 
the eye-glades almoft as broad as the palm of a man’s hand. 
Mr. Oldenburg, fecretary to the Royal Society, received 
an account of this inftrument from Rome, and read it at 
one of their meetings, Augull 6, 1668. 
But no man diftinguidied himfelf fo much by micro- 
fcopical difcoveries as the famous M. Leeuwenhoek, 
though he ufed only fingle lenfes with diort foci, prefer¬ 
ring diftinftnefs of vilion to a large magnifying power. 
Leeuwenhoek’s microfcopes were all fingle ones, each of 
them confiding of a fmall double-convex glafs, let in a 
focket between two diver plates rivetted together, and. 
pierced with a fmall hole; and the objeft was fixed on the 
point of a needle, which could be placed at any diftance 
from the lens. If the objects were folid, he fattened them 
with glue; and, if they were fiuid, or required to be fpreach 
upon glafs, he placed them on a fmall piece of Mufcovy- 
talc, or thin glafs, which he afterwards glued to a- 
needle. He had, however, a different apparatus for view¬ 
ing the circulation of the blood, which he could attach 
to the lame microfcopes. 
Leeuwenhoek bequeathed the greateft part of his mi¬ 
crofcopes to the Royal Society. They were placed in a 
fmall Indian cabinet, in the drawers of which were thir¬ 
teen little boxes, each of which contained two micro¬ 
fcopes, neatly fitted-up in lllver. The glafs of all thefe 
lenfes is exceedingly clear, but none of them magnify fo 
much as thofe globules which are frequently ufed in other 
microfcopes. Mr. Folkes, who examined them, thought 
that they fhowed objects with much greater diftinftnefs; 
a circumftance which Leeuwenhoek principally valued. 
His difcoveries, however, are to be afcribed not fo much 
to the goodnefs of his glaffes, as to his great experience 
in ufing them. Mr. Baker, who alfo examined thefe mi¬ 
crofcopes, and reported concerning them to the Royal 
Society, found that the greateft magnifier enlarged the 
diameter of an objeft about 160 times, tyut that all the 
reft fell much fhort of that power. He therefore con¬ 
cluded, that Leeuwenhoek mull have had other micro¬ 
fcopes of a much greater magnifying power for many of 
his difcoveries. 
It appears, from Leeuwenhoek’s w'ritings, that he was 
not unacquainted with the method of viewing opaque ob- 
jedts by means of a fmall concave reflefting mirror, which 
was afterwards improved by M. Lieberkhun. For, after 
defcribing his apparatus for viewing eels in glafs tubes, 
he adds, that he had an inftrument to which he fcrewed 
a microfcope fet in brafs, upon which microfcope he faf- 
tened a little difli of brafs, probably that his eye might be 
thereby aflifted to fee objefts better; for he fays he had 
filed the brafs which was round his microfcope as bright as 
he dbuld, that the light, while he was viewing objefts, 
might be reflefted from it as much as poffible. This mi¬ 
crofcope, with its difh, is conftrufted upon principles fo 
fimilar to thofe which are the foundation of our fingle mi¬ 
crofcope by refieftion, that it may well be fuppofed to 
have given the hint to the ingenious inventor of it. 
In 1702, Mr. Wilfon made feveral ingenious improve¬ 
ments in the method of ufing fingle magnifiers for the 
purpofe of viewing transparent objefts ; and his micro¬ 
fcope, which is alfo a necefiary part of the folar microfcope, 
is in very general ufe at this day. 
4 ' ' The. 
