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facilities which the spectroscope furnished for ascertaining their 
physical nature. The first application of the spectroscope to a comet 
was made by Mr. Huggins in 1866, and again in 1867 and 1868, but 
not of such a satisfactory character as to diminish the interest with 
which the announcement was received of the discovery, on the 17th of 
April, by a Marseilles observer (M. Coggia), of a comet, the orbit of 
which was determined by Mr. Hind, who was of opinion that the comet 
could not have visited our system for many centuries ; its curve was 
elliptical; the period of revolution of such length as to be uncertain ; 
the semi-axis major rather more than 430 times the earth’s mean dis- 
tance from the sun ; and.the corresponding length of revolution nearly 
9,000 years. By the 23rd June the comet became easily visible to the 
eye, with a tail of about one degree in length. On the Ist July the 
tail had increased to fully 1.5 degrees ; on 4th July to 3.5 degrees ; and 
on 6th July to five degrees, in two streams, divided by a darker space ; 
on 7th July to seven degrees. Stars were seen distinctly through the 
comet, and on the 7th a small star was easily seen through its brightest 
portion. On the 8th July the tail measured ten degrees, and the 
nucleus scintillated almost like a star, arising, perhaps, from unsteadi- 
ness in our own atmosphere. By toth July the tail was more than ten 
degrees, and its sides were of equal brightness. 
On the 14th July he observed the comet from Dr. Prince’s 
Observatory, near Uckfield. Its tail was then between 25 and 26 
degrees, and the whole comet much increased in brilliancy. The 
sector, in close contact wlth the nucleus, was only to be distinguished 
from it by the superior brilliancy of the planet-like disc, there being 
no dark space between the nucleus and the sector. The ends of the 
sector were deflected on each side, and connected by streaks of light 
with the tail ; while parallel to these streaks and outside of them were 
others running towards the head, where they merged into a luminous 
hazy arc of light surrounding the sector at a short distance from it ; 
and, as far as could been seen, unconnected with it. This arc of light 
was what was termed an envelope—and a conspicuous one. Behind 
the nucleus, and commencing close to it, was a dark space, in form 
symmetrical with the outline of the comet, and traceable for some 
distance ; it was suffused with a hazy luminosity and merged into the 
general undefined light of the tail. On the 14th July, when he saw the 
comet for the last time, its tail seemed to be fully thirty degrees long, 
and Mr. Hind had given its length on the 19th July as 43.5 degrees, or 
an actual length of 25,000,000 miles. 
a 
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