The Sun.
London, England, 1858-10-28 00:00:00

THE COMET.

M. Chacornac has just communicated to the
Academy of Sciences a series of astronomical obser-
vations of the comet, commencing from the 10th
ult.- The instrument used by him was the great
equatorial of MM. Secretan and Eitchens, with
lenses magnifying from 60 to 770 times. On the
10th, the nucleus of the comet, observed with the
lowest magnifying power, appeared round and very.
brilliant. The coma which surrounded it had 0,
feeble lustre, which did not prevent the outline of
the nucleus from being well-defined, like a planetail
disc. But in proportion as the magnifying power
was increased, the appearance of the comet was ino-
dified, so that, when magnified 770 times, the nu-
cleus assumed the appearance of a nebula having
merely a concentratiion of matter in its centre. TO
the naked eye, the nucleus with its coma seemed at
least equal in size to that of the most brilliant stall
of the tail of Ursa Major; nevertheless direct ph°:
tometric comparisons have shown that the most
brilliant part of the nueleu; was inferior in lustre
to the stars of Ursa Major. On that day the light
of the comet did not offer any visible traces of po'
larisation. The coma presented nothing remark-
able ; it encircled the nucleus uniformly, without
presenting any distinct difference of lustre any-
where, and its feeble light was gradually lost IA
the dark background of the sky. On the 11th,
the comet offered nothing remarkable, except that
the southern part of the coma was somewhat more
brilliant than the northern one. On the 13th the
brilliancy of the nucleus was photometrically com-
pared with a star of the seventh or eighth magni-
tude ; on the 14th, similar observations proved that
the southern part of the coma continued to be more
brilliant than the northern one. The comet, elm,
mined with the large telescope, but without an eye 4
piece, presented, with Savart's polariscope, sore°
faint traces of polarized light, only perceptible in
the portion of the tail nearest the nucleus. On the
19th, the aspect of the comet had slightly changed,
the light of the coma having generally become more
intense. The nucleus had a more appreciable die"
meter, which seemed, even with the lowest magni'
fying power, to be surrounded with a slight nebu4
losity which was mote sensible in the direction op;
posite to the tail. With the magnifying power of
770, the nucleus did not quite lose its planetary
appearance. It did not occupy the centre of the
coma, but was nearer to the northern than to the
southern limit, but both these limits are much tOO
indistinct to be available for measurement. Toe
most luminous part of the nucleus being photorne"
trically tompared to the most brilliant star of Canes
Venatici was found to be about equal in lustre to the
weaker of the two components of that double star.
On the 23d the comet presented a remarkable sPe°'
tacle ; the nucleus was enclosed within three invo-
lucra, consisting of concentric semicircles of different
luminous intensity. The two most brilliant 0f
these were traversed by rays which were alter-
nately luminous and dull. The nucleus was not
quite in the centre, but rather removed towards the
northern side, the coma there continuing to be less
luminous than the southern one. Lastly, close to
the nucleus, a fourth involucrum was seen, more
luminous still than the preceding ones, and apPa"
rently issuing from the nucleus spiral form. On the
25th this involucrum was found to have expanded,
inckeasing its distance from the nucleus, while 0,
fifth involucrum was being formed exactly like the
fourth ; two more were gradually disengaged froca
the nucleus between Sept. 25 and Oct. 8. The sixth
was very brilliant, and yielded polarised light. 011
the 6th Oct. four small luminous clouds were spreau
over the surface of the sixth involucrum, the bril-
Haney of which was uniformly distributed on both
sides of the axis of the tail. On the 9th the' hin
ffous arc forming the seventh involucrum displayed
a small black spot, of a triangular form. See'
through the large telescope, this spot had the 01)"
pearance of a rent in the involucrum, the latter
and the nucleus being both deformed. The light
was distributed equally around the radius vector,
passing through the black spot, and at its extre-
mity it formed a kind of protuberance. This PI
tuberance was equally remarkable on the sixt
involuCrum, The light-of the' involucra and of th° -
nucleus had diminished in intensity.