the parts defigned to be examined. But none o f thofe, which
were prefented to the Royal Society, magnified fo much, as the
glafs globules, which have been ufed in other microfGopes. He
had obferved, in a letter o f his to the Royal Society, that from
upwards o f forty years experience, he found that the moll con-
fiderable difcoveries were to be made with fuch glaffes, as, magnifying
but moderately, exhibited the objeft with the moll perfeft
brightnefs and diltinfinefs. Each inftrument was devoted to one
or two objects : hence he had always fome hundreds by him. *
There is fome reafon for fuppoling, that Leeuwenhoek was acquainted
with a mode o f viewing opake objects, fimilar to that
invented by Dr. Lieberkuhn. t
About the year 1665, fmall glafs globules began to be occa-
fionally applied to the Angle microfcope, inftead o f convex lenfes.
B y thefe globules, an immenfe magnifying power is obtained.
The invention o f them has been generally attributed to M.
Hartfoeker; it appears, however, to me, that we are indebted
to the celebrated Dr. Hooke for this difcovery; for he defcribed
the manner of making them in the preface to his Micrographia
Illuftrata, which was publifhed in the year 1656. Now the firft
account we have o f any microfcopical difcovery by M. Hartfoeker,
was that o f the fpermatic animalcule, made by him
when he was eighteen years old; which brings us down to the
year 1674, long after Dr. Hooke’s publication.
As thefe glafs globules have been very ufeful in the hands
o f experienced obfervers, I fhall lay before my readers the
different
* Philofophical Tranfa£tions, No. 389, No. 458.
f Piieltley’s Hiftory of Optics, p. 220.
different modes which have been defcribed for making them, that
he may be enabled thereby to verify or confute the difcoveries
that have been faid to be made with them.
Take a fmall rod * o f the cleareft and cleaneft glafs you can
procure, free, if poffible, from blebs, veins, 'or fandy particles;
then by melting it in a lamp made with fpirit o f wine, or the
pureft and clearefl fallad oil, draw it out into exceeding fine and
fmall threads ; take a fmall piece o f thefe threads, and melt the
end thereof in the fame flame, till you perceive it run into a fmall
drop or globule o f the defired fize ; let this globule cool, then
fix it upon a thin plate o f brafs or filver, fo that the middle o f it
may be direfily over the center o f a very fmall hole made in this
plate, handling it till it is fixed, by the before-mentioned thread
o f glafs. When the plate is properly fixed to your microfcope,
and the objeft adjufted to the focal diflance of the globule, you
will perceive the objeft diftinflly and immenfly magnified. By
this means, fays Dr. Hooke, I have been able to diftinguifh the
particles of bodies, not only a million of times fmaller than a
vifible point, but even to make thofe vifible whereof a million of
millions would hardly make up the bulk o f the fmalleft vifible
grain o f fand ; fo prodigioufly do thefe exceeding fmall globules
enlarge our profpeft into the more hidden receffes of nature.
Mr. Butterfield, in making o f the globules, ufed a lamp with
fpirit o f wine; but inftead o f a cotton wick, he ufed fine filver
wire, doubled up and down like a fkain o f thread, f He pre-
B . pared
* Le&ures and Collections by Dr. Hooke,
t Philof. Tranf. No. 141.