The Express.
London, England, 1858-09-28 00:00:00

OAT

LONDON, TUESDAY EVENING, SEPTEMBER 28, 1858.

THE COMET.

its inhabitants with their habitations into
the we. It is true he gave us most
lambing aseuranoes of the thousands, nay millions,
of ohanoes there were in our favour, that no comet
whose orbit crossed that of our planet, would ever
woes that orbit selliciently near the earth to do such
damage. Still the Kim:* of probabilities is not a
very assuring one, wise we know not how many
senesta there are, and have an uncomfortable sue-
pkina that all its assurances might any day be set at
nought by some new visitor.

On the 2nd of Inns lest Dr. Donati, of Florence,
discovered a small nebulous star. A few observations
determined the character of the stranger to be that
of a comet. Theis observations were not only sun-
oiled to demonstrate the presence of a new comet,
but also to make a fair approximation to the path of
the wanderer. The comet grows in brightness, it
follows very nearly its approximate path, as alai-
bred from a few of its observed positions, till it
becomes a marked and remarkable object to the
naked eye, and now on every clear night is beheld
with wonder and pleasure by thousands.
Comparatively few of the present generation have
seen such an astronomical phenomenon. No
wonder therefore that we are assailed on all sides
by the inquiries—What are comets P When do they
oome from P Where do they go to? Are we indebted
to the comet for our present warm weather as well as
our abundant harvest and crops of fruit P What is a
perihelion passage and so on. Now there is no
lack of books or teachers to supply all this informa-
tion. But every man has not the books on his
shelves; and if they are there, he may not have
time or leisure to tarn over their pages end satisfy
his curiosity. Thom oonvereant with the facts of
Sy, and sathaelestle nests* to display their
Clore et knowledge to every listener, may not meet
these most desirous of hearing their lore. It is the
province of the press to give sound views and in-
formation on all the current events of the day, and
a chapter on comets will doubtless be aooeptable to
many of our readers.
Before the discoveries of Newton, whose statue at
his native place has been so recently inaugurated,
the stars presented several wandering bodies, whose
orbits defied the powers of calculation of the metro-
ann. These were called planets and comets. If
the planets were so named for their wandering and
erratic paths, defying the skill of the astronomer to
reduce them to rule and order, the comets were pre-
saminentlt entitled to the character of most vagrant
bodies. The meet brilliant 'planets failed to startle
or inane the terrestrial beholder, so much as
ts=tion of a star with a Tut streaming tail,
covering a sossiderable portion of the
vhlhia heavens. If the wandering planets were sup-
posed to influence the bodies and histories of men,
canto, their laming brands across the skies,
'odd bode dlig short of plague, fire, and the
sword to mother end empires.
After /eft and dreary study and most invincible
isibmtry, legine reduced the orbits of the planets
to peat simplicity, bringing them under the
artier of dine simple and exact laws. Their
vagaries amen the fixed stars, their advance, their
retregramise, their apparent stand still in their
homely isms, were all shown to arise, from the
deseptione of perspective, and from our viewing their
neer from en observatory itself in constant motion.
Besenrring to the theory of Copernicus, that the sun
we. the centre, while we, like all the other planets,
VIM revolving round that centre in orbits, Kepler
determined the true orbits which would account for
all the apparently irregular motions of the planets
amid the other heavenly bodies. Newton then stept
in with his universal law of gravitation, and showed
that Kepler's laws were the consequence of one
simple law of attraction, combined with the laws of
motwo.
Kepler suspected the comets of moving in parabo-
lic orbits, but Newton showed that they, like the
planets, are under the domain of the same physical
law. According to the Newtonian theory, irrespeo-
tire of perturbations, there are but four disuact
curves, in whisk bodice acted upon by the laws of
gravitation can move. These are all found
in the sections of a cone. 8o far as observation
has been extended, it is doubtful whether in point
of fact all the observed orbits are not confined to one
'peeler, the ellipse. The ellipse is an oval figure,
which mat of our readers may have seen described
over and over again, while watching a gardener
laying out an oval Hower bed. He sucks two pegs
of wood firmly in the ground, he ties the extremities
of a piece of cord together, he throws his loose ring
of cord over the two pegs, and then with a stick, he
stretches the cord over the pegs, and marks on the
ground the line which his suck follows while he
walks round keeping the cord always stretched to
its utmost extent. In this way he marks oat an
oval line or boundary, perfectly symmetrical. This
oval is a geometrical ellipse, and the two pegs are
called its foci. According to the observation of the
motions of planets and comets neglecting minute
deviations caused by the disturbing influences which
they exert on sack other, this oval is the orbit
of all or nearly all that have been observed or
calculated. If with a cord of given length the two
pegs over which the cord is stretched, or the two
foci, are made to apprcach very near each other, the
oval approaches closely to the figure of the circle.
Indeed, if the two pegs accurately coincided, it
would be a circle. All the planets move in ellipses
very nearly circular, or in ellipses of small eicentri-
ray. The sun is always in one of the foci of the
orbit. I,f, on the other hand, the foci be placed at •
considerable distance from each other, the figure is
more oval in its character, its eccentricity is greater,
and we have the orbit of a comet. As the nearer
the foci of the ellipse approach each other, the more
the ellipse approaches the form of the oirole, so the
more they diverge from each other the more the
ellipse approaches to another curve, called the
parabola, which is also a conic section. Mathe-
matically speaking a parabola is as ellipse tits dis-
tance of whose foci is ityterely grunt.
According to the Newtonian laws, there is only
this differanos between planets and oomets—that
while the former are moving in orbits nearly cir-
cular, the latter revolve in orbits of greater eocen-
tricity—in ellipses, or perhaps in parabolas or hyper-
bolas. Theoretically they might move either in pa-
rabolas or hyperbolas ; but then after one visit to
lour system, they could never return again. As in
the ass of the planets, so in that of comets, the
polities of the ran is always in one of these foci.
Modern science, therefore, to a certain extent, de-
nudes the oometary appearanoee of the vague terrors
they once excited. They are reduced to the level of
trek ordinary attendants of the solar system as the
planste—ruled by the same laws. Doss edam sug-
gest no real terrors in place of the vague fears of
ignorance? The paths of the planets being nearly
circular—nearly all in the same plane—their dis-
tances from each other vast, and the son near the
centre of their orbits, no fear exists that they can
ever arc= each other's path and oome into collision.
It is not so with comets ; they whirl round the son
in every possible direction : the planets all move
royal an way, and not far removed from
oss imaginary surface or plane; the anew
MIMS in every plane, and some in the direction of
the planets, and others in the opposite. Fur an
thing, tier.. .., that can be determined, either some
coast which has not visited our system within
historic period, or some one whose path has bees
asnueminod, might oorne into collision with a planet.
What would be the effect of this collision is indeed
a stsrtling gelation, and one not easily answered.
Whine assented for the universal Deluge by sup-
pain ow planet involved in the tail of a passing
comet. This may be said to be the vague surmise of
an imaginative individual, not the determination of
a sound mathematical and physical philosopher.
Tot Lalande, the astronomer and calculator of
cossetery orbits, dessribing, in 1773, what would be
the effect of a coat prang within 46,000 miles of
the forth, thatch be could me no danger of so MST a
proximity, so frightened the Parisians that many died
of sheer terror. The passage of a cornet so near
the earth would, he thought, raise the waters
of the cease to such a height, they would sweep
ow the spoodesat of Europe, and carry all

Supposing a comet to be a heavy solid mass fo
matter, La I'laos has amused himself by speculating
upon the probable effects of a collision upon the
earth. These are, a change of the position of the
axis of the earth's rotation and motion. This would
bring about a. complete alteration of the relation of
sea and land—laying the beds of the present great
mean bare, and covering the present continents with
the water, and changing the climate of every part
of the globe.
Them are terrors great enough fp counterbalance
all the vague fetus of the ancients, ter of the present
uncultivated nations of the earth. Has seism no
consolation to offer in the place of the barest shadow
of a chance of so dire a catastrophe P The possibility of
these dread changes of the ocean's bed, or of the refl
of her waters, depends upon the assumption of the
comets being similar in the density and the concen-
tration of their matter to those of the planets. Now,
every observation yet made on the constitution of
the esiots memo to yrove that they are destitate of
any said nucleus. They appear to be vast masses
of vapour, the particles of which are held at such a
distaste from each other, by some unknown law of
=iso, that though the tails of some of these
ham been calculated of such a length as to
be salleisnit to mach from the earth to the sun, and
some atoms beyond, it is doubtful whether if all of
me daises Mims of vapour were condensed in the
month's atmosphere it would do more than produce a
gomthe shower for a few minutes. Stars of the most
minute SW have been seen to shine with undimi-
nished holm not only through the diffused tails, but
even through the mitre of the denser head of comets.
And, what is of still further importance, a comet',
has been known to sweep. through the sphere of
Jupiter's =Wins without in any way deranging
their mafioso. The orbit of the comet wee altered
by its peoximtty to Jupiter and his satellites, while
none of those bodies experienced the slightest appre-
ciable change of motion or disturbance. Now, when
we remember that our instruments are so minute and
accurate in their powers of measurement, and our
powers of calculation so refined, that we ean find a
distant and unknown planet by the inflames it ex-
erts, by the perturbations it produces an the knave
planets, we may readily believe how insignidesnt
must have been the mass of the comet compared with
that of Jupiter, though the particles of its mass may
have been extended a million of times more through
These considerations are sufficient to reassure us
and to show that scientific warrant for alarm of Lay
mischief to be apprehended from the collision of a
amok with our planet is as vague as the more igno-
rant dread of the uninformed. We may therefore
view without apprehension these beautiful members
of oar solar system. In 1832 Biela's comet crossed
the path of the earth a month before the earth
meshed the point of intersection of the orbits.
Other comets of greater size have approached more
1 nearly to us. Humboldt thinks it probable that both
•
lin 1819 and 1823 the tails of comets mingled with
our atmosphere, yet we felt no inconvenience from
mob a near approach of oometary masses.
_ .

So far, therefore, as we know at present, comets
consist of masses of vapour diffused t.rh a great
extent of space, held together by unknown laws,
but the whole semi obedient to the laws of gravita-
tion, differing widely from one another both in
;tamers' appearance, And in the extent and
of their -orbits. Yea as we know to
the eentisry their numbers may be countless as the
dare of heaven. The paths of about a hundred and
arty have been calculated. Observations of appa•
rent courses of some six or seven hundred may be
found scattered among ancient and modern records.
Some three or four, mostly too small or distant to be
seen by the naked eye, are discovered by astronomers
every year, and have their paths noted, calculated,
and recorded.

The vapoury mass of a comet sweeps round the
sun, for the most part in elliptic orbits, having the
sun in one of the foci of the ellipse. The speed with
which the comet cleaves through space is not uni-
form. According to the law of gravity, this speed
must increase se it nears the sun, being greatest when
it is nearest the sun, and diminishing as it departs
from it according to a simple and beautiful law. By
the calculation, of Eucke, the colossal comet of 1880,
which marks the epoch of Newton's grand disco-
veries, takes a period of 8,800 years to complete its
revolution round the sun. This comet swept round
the sun with such velocity that when nearest that
body its rate was 212 miles per second, thirteen
times mater than that of the earth. When
it attains its greatest distance from the sun
it will be forty-four times farther from it
than Uranus, and its speed will be diminished to
scarcely ten feet per second. For the most part as
meets near the sun they cast forth from themselves
mesa of vapour of even greater tenuity than
their bodies ; them tails or brushes of vapour are
generally turned from the sun. As the comet ap-
proachee the sun the tail follows the comet; se it
recedes from the luminary the tail precedes the head.
The tails are sometimes carved, sometimes branched,
and change most perceptibly even foe the same
comet from day to day.
Whether comets shine by their own light, or alto-
gether by the reflected light of the sun, is still un-
determined, though Arsgo'e observations by means
of polarised light tend to show that they owe their
lustre, in great measure, if not altogether, to the bor-
rowed light of the sun.
Bailey, the friend of Newton, was the first to pre-
dict the return of a comet. He wee struck by the
similarity between the elements, obtained from the
recorded position of the comets of 1468, 1631,
and 1617, with the comet of 1882, observed
by himself. He supposed all these comets to
be ideatioal, and calculating the orbit of this
body Irspedieted its return in the year 1757 or
1758. He would not pledge himself to the exact
period of its re-appearance, because he rightly judged
that it would have its period lengthened by the
influence of the attractions of Jupiter and Saturn.
With incredible labour Clairaut, the French maths-
maticiaa,calculated the influence of these two planets
on the comet. He concluded that Jupiter would
delay its appearance 610 days, and Saturn 100. As
the comet had passed its Perihelion, that is, its
nearest point to the sun, on the 14th of September,
1882, it ought, according to M. Clairaut, to pant
the same pant of its path on the 13th of April,
1769. The verification of Clairaut's calculations,
which he said admitted, if he had had time, of
further improvement, were impatiently waited for
by the astronomers of Europe. The comet, to the
delight of all, re-appeared about the end of De-
cember, 1758, and arrived at its perihelion 011 the
13th of March, 1769, only 30 days before the time
fixed by Clainat.

The next ppee
aranae of this comet was in 1835,
when it reached its perihelion within three days of
the time predicted by the beat calculators. Mr.
Hind and M. Login have made calculations which
Wooed them to believe that the comets recorded in
MOM and European annals as having been seen in
the 218, 218. 295, 451, and 760 were visits of
comet to our system. Though the paths of
many
_comets have been calculated, only two well-
decided instances of comets whose returns can *be
predicated with certainty have been discovered
mos that of Halley. On the 28th November, 1818,
Pens, at Maneilles, discovered a comet; as usual on
the discovery of a comet a parabolic orbit was ellen-
laud for the new visitor. The reason why parabolic
orbits are ealeulated first for comets, and why they
are sa goaarally said to revolve is parabola@