tunity of making observations which led to his
discovery that comets describe orbits round the Sun in conformity with
the different sections of a cone. The comet of 1811 was observed for
many weeks in the northern heavens as a brilliant object with a
beautiful fan-shaped tail; it completes a revolution of its orbit in
about 3,000 years. The comet of 1843 was also a splendid object. It
possessed a tail 200 million miles in length, and approached within
32,000 miles of the Sun. The heat to which it was exposed was sufficient
to volatilize the most infusible substances known to exist. Donati's
comet of 1858 will be long remembered as one of the most impressive of
celestial spectacles: its tail extended over an area of forty degrees,
and enveloped the star Arcturus, which could be seen shining through it
with undiminished brilliancy. Its period is estimated to be 2,100 years.
A great comet appeared in 1861, through the tail of which the Earth
passed without any perceptible effect having resulted. No remarkable
comets have appeared during recent years. In 1880, 1881, and 1882,
several were observed, and that of 1881 was the first successfully
photographed.

Comets consist of cosmical matter which exists in a condition of extreme
tenuity, and especially so in the coma and tail. Sir John Herschel
described them as almost spiritual in texture, and small stars have been
seen shining through their densest parts without any perceptible
diminution of their light. The nucleus is believed to be composed of a
congeries of meteoric fragments, and these, when exposed to the Sun's
heat, throw off luminous nebulous particles that are swept by some
repulsive force into space and form the appendage known as the tail.
Comets may be regarded as celestial objects that are perfectly
innocuous. Neither fear nor dread need be apprehended from their visits;
they come to please and instruct, not to injure or destroy.

Milton does not fail to introduce into his poem several allusions to
comets, and in doing so expresses the ideas and sentiments which in his
time were associated with those objects.

In describing the hostile meeting between Satan and Death before the
Gates of Hell, he writes:

On the other side,
Incensed with indignation, Satan stood
Unterrified, and like a comet burned,
That fires the length of Ophiuchus huge
In the arctic sky, and from his horrid hair
Shakes pestilence and war.-