yet be seen, by the dwellers in the southern
hemisphere only, until January or February
next. The temptation to cross the line and
follow it must be great with hearty astronomers.
It will therefore have remained visible
to the earth for a total period of more than
eight months. It is in no hurry to quit
our neighbourhood; retiring, both from the
earth and the sun, at no very rapid pace.
Monsieur Babinet, of the Institute of France,
demonstrates clearly the small quantity of
matter contained in a comet; and that they
are powerless for good or evil. A well-
founded opinion admits that they are
collections of matter so extremely light as
to be unable to draw near to them, by the
force of attraction, the portion which forms
the immense appendix of their tails, which,
in consequence of some unexplained cause,
are turned in the direction opposite to the
sun. Up to the end of the month of October,
the change in the direction of the comet's
tail offers an important subject for the
observation of astronomers. About this, if
there is much to say, there remains still
more to learn.

From the eighteenth of September, the
comet displayed very singular manifestations
of luminosity. The intensity of the
brightness of the tail, hitherto uniform
or sensibly the same throughout its whole
breadth, became greater towards the centre.
On the same day, a sort of luminous phase in
the nucleus was observed. The luminous
envelopes detached themselves from the
nucleus in the form of spirals, which soon
became more and more separated from the
central body, and formed close and narrow
curves, which finally opened and assumed a
parabolic form. In proportion as these luminous
arcs were further removed from the
nucleus, they gradually lost their splendour
and at last disappeared in the confused light
of the edge of the tail. On the twenty-third
of September, Monsieur Bulard, an astronomical
draughtsman, and also Messieurs Faye
and Babinet, saw a luminous ring that had
formed itself round the comet, which had
then become smaller. This ring was imperfect,
and was interrupted on the side opposite
to the sun. Afterwards, it assumed the shape
of a bright crescent, in the interior of which
the nucleus was observed to be small, oval,
and brilliant. On the twenty-eighth, the
luminous crescent had considerably dilated,
and resembled a large fan, with a sharp horn
at each of its extremities. The head of the
comet then appeared to be surrounded with
a very distinct beard, and the appearance
lasted for several nights.

The evening of the fifth of October will
remain memorable to star-gazers. Several
thousand years may pass away before a
similar spectacle is offered to our admiration.
Between half-past six and half-past
seven, the comet passed before and a little
below the brilliant star Arcturus, which
continued to twinkle with a splendour
undliminished by the shining veil.

Donati's comet has had the effect of raising
the telescopic comets to a certain importance
in the popular opinion. Not long since, a Parisian
street-astronomer offered to his eager
customers, at eight o'clock in the evening, the
hazy comet of Monsieur Faye, which did not
rise till ten that night. Monsieur Babinet,
happening to take a peep, discovered that the
substitute offered to passers-by was the
beautiful nebula in Andromeda: putting the
annoyance of being deceived out of the question,
the public lost nothing in the quality of
the goods retailed to them.

It is to be hoped that the numerous observations
made in all the observatories of every
country, as well as by a great many amateurs,
will furnish new elements for clearing up the
question, still so obscure, as to what is the
veritable physical constitution of the comets,
and what part they play in the economy of
the universe. Rarely have astronomers had
a more complete and favourable opportunity
of studying this class of celestial phenomena;
for the year eighteen hundred and fifty-eight
has been more propitious, in this respect,
even than the year eighteen hundred and
eleven.

Monsieur Porro's observations, made in
conjunction with Monsieur Pigorini, are very
interesting. Monsieur Porro believes with
Zantedeschi that the universe is a compound
of matter which disperses itself, and matter
which conglomerates itself. The hypothetical
ether, whose existence is necessary for the
explanation of the undulatory theory of light, is
nothing else, they say, than matter in its most
extreme state of diffusion. Monsieur Porro
thinks that between this state, and that which
matter assumes in the shape of our most
rarefied gases, there exist intermediate states
of matter, of which the comets, the nebulæ,
and perhaps the zodiacal light, are examples.
Humboldt thinks that the comets are the
most ancient of all the planetary bodies, and
that they form, so to speak, the original type
of the diffuse matter which fills the heavenly
spaces.

The cosmic matter of the comets is in two
different states, both intermediate between the
ethereal and gaseous states. The matter
composing the nucleus, and the matter composing
the air-like envelope of comets, differ from each
other at least as much as the solid matter of the
terrestrial globe differs from its atmospheric
envelope. Matter in this state, according to
Monsieur Porro, is incapable of reflecting the
solar light specularly. This idea is contrary
to Arago's observation of Halley's comet
with a polariscope. Arago saw in the field of
his instrument two images offering
complementary colours, one red, the other green.
He thence concluded that the light of the
comet was not, at least entirely, composed of
rays endowed with the properties of direct
light. He found in it light reflected