The image was
first thrown upon an inclined mirror and then reflected upwards to a
paper screen on the top of the box. In an earlier form the image is
thrown upon a vertical thin paper screen and viewed through a hole in
the back of the camera. There is a great deal of practical information
on lenses in connexion with the camera and other optical instruments,
and the book is valuable as a repertory of early practical optics, also
for the numerous references to and extracts from previous writers. An
improved edition was published in 1702.

Most of the writers already noticed worked out the problems connected
with the projection of images in the camera obscura more by actual
practice than by calculation, but William Molyneux, of Dublin, seems to
have been the first to treat them mathematically in his _Dioptrica Nova_
(1692), which was also the first work in English on the subject, and is
otherwise an interesting book. He has fully discussed the optical theory
of the dark chamber, with and without a lens, and its analogy to the
eye, also several optical problems relating to lenses of various forms
and their combinations for telescopic projection, rules for finding
foci, &c. He does not, however, mention the camera obscura as an
instrument in use, but in John Harris's _Lexicon Technicum_ (1704) we
find that the camera obscura with the arrangement called the "scioptric
ball," and known as _scioptricks_, was on sale in London, and after this
must have been in common use as a sketching instrument or as a show.

Sir Isaac Newton, in his _Opticks_ (1704), explains the principle of the
camera obscura with single convex lens and its analogy with vision in
illustration of his seventh axiom, which aptly embodies the correct
solution of Aristotle's old problem. He also made great use of the
simple dark chamber for his optical experiments with prisms, &c. Joseph
Priestley (1772) mentions the application of the solar microscope, both
to the small and portable and the large camera obscura. Many patterns of
these two forms for sketching and for viewing surrounding scenes are
described in W.J.'s Gravesande's _Essai de perspective_ (1711), Robert
Smith's _Compleat System of Optics_ (1738), Joseph Harris's _Treatise on
Optics_ (1775), Charles Hutton's _Philosophical and Mathematical
Dictionary_, and other books on optics and physics of that period. The
camera obscura was first applied to photography (q.v.) probably about
1794, by Thomas We