y told nothing. No lines were
visible in them. They were mere characterless streaks of light. Nine
years later Dr. Henry Draper of New York got an impression of four lines
in the spectrum of Vega. Then Huggins attacked the subject again in
1876, when the 18-inch speculum of the Royal Society had come into his
possession, using prisms of Iceland spar and lenses of rock crystal; and
this time with better success. A photograph of the spectrum of Vega
showed seven strong lines.[1415] Still he was not satisfied. He waited
and worked for three years longer. At length, on December 18, 1879, he
was able to communicate to the Royal Society[1416] results answering to
his expectations. The delicacy of eye and hand needed to obtain them may
be estimated from the single fact that the image of a star had to be
kept, by continual minute adjustments, exactly projected upon a slit
1/350 of an inch in width during nearly an hour, in order to give it
time to imprint the characters of its analyzed light upon a gelatine
plate raised to the highest pitch of sensitiveness. But by this time he
had secured in his wife a rarely qualified assistant.

The ultra-violet spectrum of the white stars--of which Vega was taken as
the type--was thus shown to be a very remarkable one. A group of broad
dark lines intersected it, arranged at intervals diminishing regularly
upward, and falling into a rhythmical succession with the visible
hydrogen lines. All belonged presumably to the same substance; and the
presumption was rendered a certainty by direct photographs of the
hydrogen spectrum taken by H. W. Vogel at Berlin a few months
earlier.[1417] In them seven of the white-star series of grouped lines
were visible; and the full complement of twelve appeared on Cornu's
plates in 1886.[1418]

In yellow stars, such as Capella and Arcturus, the same rhythmical
series was _partially_ represented, but associated with a great number
of other lines; their state, as regards ultra-violet absorption,
approximating to that of the sun; while the redder stars betrayed so
marked a deficiency in actinic rays that from Betelgeux, with an
exposure _forty times_ that required for Sirius, only a faint spectral
impression could be obtained, and from Aldebaran, in the strictly
invisible region, almost none at all.

Thus, by the means of stellar light-analysis, acquaintance was first
made with the ultra-violet spectrum of hydrogen;[1419] and its harmonic
character, as expresse