Helmut Gernsheim & Alison Gernsheim, The History of Photography: From the Camera Obscura to the Beginning of the Modern Era

34 The prehistory of photography
of the invisible ultra-violet rays : 'It is by their chemical effects alone', he wrote,18
'that the existence of these can be discovered ; and by far the most delicate test of
their presence is the white muriate [chloride] of silver.'
From that time on, the rays beyond the violet, which are, as Ritter and W ollaston
pointed out, chemically the most effective, were called 'the chemical rays' to differentiate
them from the luminous rays which are chemically far less effective, as Senebier
had already shown in his table.
Whereas these scientists carried Schulzc's and Scheele's experiments farther to
widen their knowledge of the nature of light, a large number of books of popular
scientific entertainment which appeared in the latter half of the eighteenth century
included Schulze's experiment simply as an amusing recreation. The first of these
is Guyot's four-volume Nouvelles Recreations (1769-70) which was translated into
German and English-for Dr William Hooper's Rational Recreations (1774) is not an
original work but virtually a translation of Guyot's book-a fact which has not to
our knowledge been pointed out before. Hooper's four-volume Rational Recreations
enjoyed no less popularity than Guyot's, further editions being published in 1782,
1783, and 1787. Taking the first edition of 1774 we find Schulze's experiment in
vol. iv under the title 'Writing on glass by the rays of the sun' ; and in following
years this recreation was reprinted verbatim in Kearsley's Pocket Ledger. Hellot's
method of secret writing with nitrate of silver is also given in Guyot and Hooper.
It would be tedious to list all the publications containing Schulze's experiment. It was
widely disseminated in France, Germany, and England, and it did not, therefore,
require a great deal of imagination to apply it to picture-making, though curiously
enough none of the scientists engaged on investigations into the chemical change of
silver salts under the influence of light seems to have thought of making practical use
of it, in the sense of trying to cause the sun's rays to make impressions of objects,
portraits, or landscapes. The first person to whom the idea of Nature-printed pictures
occurred was not a scientist but a writer of fiction.