From this period, to the year 1736, the microfcope appears
not to have received any confiderable alteration, but the
fcience itfelf to have been at a {land. The improvements which
were making in the reflefting telefcope, naturally led thofe who
had turned their thoughts this way, to expea a fimilar fervice
for microfcopes on the fame principles: accordingly we find two
plans o f this kind; the firfi was that o f Dr. Robert Barker.
This inftrurnent is entirely the fame as the reflefting telefcope*
excepting thè diftanee o f the two fpeculums, which lengthened*
in order to adapt it to thofe pencils o f rays which enter the
telefcope diverging; whereas, from very diftant objefts, they
come in a direftion nearly parallel. But this was foon laid afide,
not only as k was more difficult to manage, but alfo becaufe it
was unfit for any but very fmall or tranfparent objefts: for the
objeft being between the fpeculum and the image, would, i f it
were large and opake, prevent a due refleftion o f light on the
objeft.
The fecond was contrived' by Dr. Smith * In this there were
two reflefting mirrors, one concave, and the other convex; the
image was viewed by a lens. This microfcope, though far from
being executed m the beft manner, performed, fays Dr. Smith,
very well, fo that he did not doubt but what it would have excelled
others, if it had been properly finiffied.
As feme years are more favorable to the fruits o f the earth, fo
alfo fome periods are more favorable to particular fciences, being
rich in difcovery, and cultivated with ardor. Thus, in the year
6 1738,
* Dr. Smith’s Optics, Remarks, p.94.
i c r o s c o p i c a l E s s a y s . to
1738, Mr. Lieburkuhn’s invention o f the folar microfcope was
communicated to the public : the vaft magnifying power which
was obtained by this inllrument, the coloflal grandeur with which
it exhibited the minima o f nature, the pleafure which arofe from
being able to difplay the fame objeft to a number of obfervers at
the fame time, by affording a new fource o f rational amufement,
increafed the number o f microfcopic obfervers, who were further
ftimulated to the fame purfuits by Mr. Trembley’s famous difcovery
o f the polype: the wonderful properties of this little animal,
together with the works o f Mr. Trembley, Baker, and my father,
revived the reputation o f this inftrurnent. *
Every optician now exercifqd his talents in improving (as he
called it) the microfcope; in other words, in varying it’s con-
ftruftion, and rendering it different frqm that fold by his neighbour.
Their principal objeft feemed to be, only to fubdivide
the inftrurnent, and make it lie in as fmall a compafs as poffible ;
by which means, they not only rendered it complex, and trou-
blefome in ufe, but loft fight alfo -of the extenfive field, 'great
light, and other excellent properties o f the more ancient inftru-
ments; and in fome meafure, {hut themfelves out from further
improvements on the microfcope. Every mechanical inftrurnent
is fufceptible o f almoft infinite combinations and changes, which
are attended with their relative advantages and difadvantages:
thus, what is gained in power, is loft in time; “ he that loves to
be confined to a fmall houfe, muft lofe the benefit o f air and
exercife.”
C 2 The
* Trembley Memoires fur les Polypes. Baker’s Microfcope made Eafy;
Attempt towards an Hiftory of the Polype,; Employment for ,the Microfcope.
Adams’s Micrographia UluErata. Joblot’s Obfervations d’Hiftoire Naturelle.