t in the one case, dark in the
others, since identified as a member of one of the helium series.

The structural unity of the stellar and nebular orders in this extensive
region of the sky has also, by direct photographic means, been
unmistakably affirmed.

The first promising autographic picture of the Orion nebula was obtained
by Draper, September 30, 1880.[1542] The marked approach towards a still
more perfectly satisfactory result shown by his plates of March, 1881
and 1882, was unhappily cut short by his death. Meanwhile, M. Janssen
was at work in the same field from 1881, with his accustomed
success.[1543] But Dr. A. Ainslie Common left all competitors far behind
with a splendid picture, taken January 30, 1883, by means of an exposure
of thirty-seven minutes in the focus of his 3-foot silver-on-glass
mirror.[1544] Photography may thereby be said to have definitely assumed
the office of historiographer to the nebulae, since this one impression
embodies a mass of facts hardly to be compassed by months of labour with
the pencil, and affords a record of shape and relative brightness in the
various parts of the stupendous object it delineates which must prove
invaluable to the students of its future condition. Its beauty and merit
were officially recognised by the award of the Astronomical Society's
Gold Medal in 1884.

A second picture of equal merit, obtained by the same means, February
28, 1883, with an exposure of one hour, is reproduced in the
frontispiece. The vignette includes two specimens of planetary
photography. The Jupiter, with the great red spot conspicuous in the
southern hemisphere, is by Dr. Common. It dates from September 3, 1879,
and was accordingly one of the earliest results with his 36-inch, the
direct image in which imprinted itself in a fraction of a second, and
was subsequently enlarged on paper about twelve times. The exquisite
little picture of Saturn was taken at Paris by MM. Paul and Prosper
Henry, December 21, 1885, with their 13-inch photographic refractor. The
telescopic image was in this case magnified eleven times previous to
being photographed, an exposure of about five seconds being allowed; and
the total enlargement, as it now appears, is nineteen times. A trace of
the dusky ring perceptible on the original negative is lost in the
print.

A photograph of the Orion nebula taken by Dr. Roberts in 67 minutes,
November 30, 1886, made a striking disclosure of the extent of that
prod