P. Bond. One of the best of these is reproduced on Plate
XVII., p. 256.

In 1861 there appeared a great comet. On the 30th of June of that year
the earth and moon actually passed through its tail; but no effects were
noticed, other than a peculiar luminosity in the sky.

In the year 1881 there appeared another large comet, known as Tebbutt's
Comet, from the name of its discoverer. This was the _first comet of
which a satisfactory photograph was obtained_. The photograph in
question was taken by the late M. Janssen.

The comet of 1882 was of vast size and brilliance. It approached so
close to the sun that it passed through some 100,000 miles of the solar
corona. Though its orbit was not found to have been altered by this
experience, its nucleus displayed signs of breaking up. Some very fine
photographs of this comet were obtained at the Cape of Good Hope by Mr.
(now Sir David) Gill.

The comet of 1889 was followed with the telescope nearly up to the orbit
of Saturn, which seems to be the greatest distance at which a comet has
ever been seen.

The _first discovery of a comet by photographic means_[25] was made by
Professor Barnard in 1892; and, since then, photography has been
employed with marked success in the detection of small periodic comets.

The best comet seen in the Northern hemisphere since that of 1882,
appears to have been Daniel's Comet of 1907 (see Plate XVIII., p. 258).
This comet was discovered on June 9, 1907, by Mr. Z. Daniel, at
Princeton Observatory, New Jersey, U.S.A. It became visible to the naked
eye about mid-July of that year, and reached its greatest brilliancy
about the end of August. It did not, however, attract much popular
attention, as its position in the sky allowed it to be seen only just
before dawn.

[24] With the exception, of course, of such an anomaly as the retrograde
motion of the ninth satellite of Saturn.

[25] If we except the case of the comet which was photographed near the
solar corona in the eclipse of 1882.

[Illustration: PLATE XVIII. DANIEL'S COMET OF 1907

From a photograph taken, on August 11th, 1907, by Dr. Max Wolf, at the
Astrophysical Observatory, Heidelberg. The instrument used was a 28-inch
reflecting telescope, and the time of exposure was fifteen minutes. As
the telescope was guided to follow the moving comet, the stars have
imprinted themselves upon the photographic plate as short trails. This
is clearly the opposite to what is depicted on Plate XI