only that sufficient light came from it. The experiments it
recorded might be performed in the sun, or in the most distant
stars or nebulae; indeed, one of the earliest feats of the
instrument was to wrench from the sun the secret of his chemical
constitution.

To render the utility of the spectroscope complete, however, it
was necessary to link with it another new chemical
agency--namely, photography. This now familiar process is based
on the property of light to decompose certain unstable compounds
of silver, and thus alter their chemical composition. Davy and
Wedgwood barely escaped the discovery of the value of the
photographic method early in the nineteenth century. Their
successors quite overlooked it until about 1826, when Louis J. M.
Daguerre, the French chemist, took the matter in hand, and after
many years of experimentation brought it to relative perfection
in 1839, in which year the famous daguerreotype first brought the
matter to popular attention. In the same year Mr. Fox Talbot read
a paper on the subject before the Royal Society, and soon
afterwards the efforts of Herschel and numerous other natural
philosophers contributed to the advancement of the new method.

In 1843 Dr. John W. Draper, the famous English-American chemist
and physiologist, showed that by photography the Fraunhofer lines
in the solar spectrum might be mapped with absolute accuracy;
also proving that the silvered film revealed many lines invisible
to the unaided eye. The value of this method of observation was
recognized at once, and, as soon as the spectroscope was
perfected, the photographic method, in conjunction with its use,
became invaluable to the chemist. By this means comparisons of