The earliest magnifying lens of which we have any knowledge was one
rudely made of rock-crystal, which Mr. Layard found, among a number
of glass bowls, in the north-west palace of Nimroud; but no similar
lens has been found or described to induce us to believe that the
microscope, either single or compound, was invented and used as an
instrument previous to the commencement of the seventeenth century.
In the beginning of the first century, however, Seneca alludes to the
magnifying power of a glass globe filled with water; but as he only
states that it made small and indistinct letters appear larger and more
distinct, we cannot consider such a casual remark as the invention of
the single microscope, though it might have led the observer to try the
effect of smaller globes, and thus obtain magnifying powers sufficient
to discover phenomena otherwise invisible.
Lenses of glass were undoubtedly in existence at the time of Pliny;
but at that period, and for many centuries afterwards, they appear
to have been used only as burning or as reading glasses; and no
attempt seems to have been made to form them of so small a size as
to entitle them to be regarded even as the precursors of the single
microscope.--_North-British Review_, No. 50.
The _rock-crystal lens_ found at Nineveh was examined by Sir
David Brewster. It was not entirely circular in its aperture. Its
general form was that of a plano-convex lens, the plane side having
been formed of one of the original faces of the six-sided crystal
quartz, as Sir David ascertained by its action on polarised light:
this was badly polished and scratched. The convex face of the lens
had not been ground in a dish-shaped tool, in the manner in which
lenses are now formed, but was shaped on a lapidary’s wheel, or in
some such manner. Hence it was unequally thick; but its extreme
thickness was 2/10ths of an inch, its focal length being 4½ inches.
It had twelve remains of cavities, which had originally contained
liquids or condensed gases. Sir David has assigned reasons why this
could not be looked upon as an ornament, but a true optical lens.
In the same ruins were found some decomposed glass.