Edwardsville spectator. [volume] (Edwardsville, Ill.) 1819-1826, 1819-09-18

1 be mere collections OF vapours condenS-
ed about centre. Five more were OBJ
served by himself, which were nearly of
the same nature. This circumstance,
he says, " throws mystery over their
destination, which seems to place them
in the categorical view oftools, probably
designed for some salutary purposes to
be wrought by them; and whether tho
restoration of what is lost to the sun by
the emission of light may not be one Of
those purposes, l shall not presume to
determine. The motion of the comet
discovered by Mr.. Messier, June l77o,
plainly indicated how much its orbit was
liable to be changed by the perturbation
of the planets, from which, and the little
agreement that can be found between
the elements of the orbits of all the CO.
NETS that have been observed, it appears
clearly that they may be directed to carry
their salutary influence to any part of the
heavens"
1t is extremely difficult to determine.
from computation, the elliptic orbit of a CO.
met to any degree of accuracy; for when
! the orbit IS very eccentric, very small
error in the observation will change the
computed orbit into parabola or hyper
bola. Now, from the thickness and in
equality OF the atmosphere with which
the comet is surrounded, it is impossible
to determine with any great precision
when either the limb or the centre of the
comet pass the wire at the time of obser-
walton. And this uncertainty in the OBJ
servations will subject the computed Or
bit to great error. Hence it happen-
ed that M. Bouguer determined the orbit
of the comet in l7l9 to be an hyperbola.
M. Euler determined the same for the
comet in l744; but having received
more accurate observations, he found it
to be an ellipse. The period of the CO.
met in 1850 appears from observation
to be SIS years, which M. Euler by his
computation determined to be 1864 years.
Such is the uncertainty that prevails in
regard to the calculation of the orbits of
comets! The only probable way to OBJ
tain the period of comets, is to compare
the elements of all those which have been
computed, and where you find that they
agree very well you may conclude that
they are elements of the same comets
it being SO extremely improbable that
the orbits OF two different comets should
have the same inclination, the same PEE
rihelion distance, and the places of tho
perihelion and node the same. Thus
knowing the periodic time, we get the
greater axis of the ellipse; and the PEI
rihelion distance being known, the lesser
axis will be known. When the ele-
ments of the orbits agree, the comets may
be the same, although the periodic times
should vary little; as that may arise
from the attraction of the bodies in our
system, and which may also alter all the
other elements little.
There have been various coniectures
about the tails of comets. Apian, Car
den, Tycho Brahe, supposed that they
were produced by the suns rays trans
mitted through the nucleus of the comet,
which they suppose to be transparent,
and there refracted, as in a lens of glass,
so as to form beam of light behind the
comet. Kepler supposed, that the rays
of the sun carry away some of the gross
parts Of the comet which reflect the suns
rays, and give the appearance of tail.
Hevelius thought, that the thinnest parts
of the atmosphere of comet are rare
fled by the force of the heat, and driven
from the fore part and each side of the
comet towards the parts turned from the
sun. Des Cartes accounted for the phe-
nomenon of the tail by the refraction of
of light from the head of the comet to
the eye Of the spectator. Sir Isaac New
ton supposed the tails of comets to be
vapor, produced from the atmosphere
of the comet by the heat of the sun. Ma
rian thought that the tails were formed
out Of the luminous matter that composes
the SUMS atmosphere. M. Euler thinks
there is great affinity between the tails
of comets, the zodiacal light, and the
aurora boreals, and that the common
cause of them all, is the action of the
suns light on the atmosphere of the CO.
NETS, of the sun, and of the earth.
DR.. Hamilton, of Glasgow, urges Sc
veral objections against the Newtonian
hypothesis; observing, that we have no
proof of the existence of a solar atmos-
phere; ard if we had, that when the CO.
met is moving in its periheiiop, in direc-
ton at right angles to the direction of its
tail, the vapors which then arise partak-
ing of the great velocity of the comet,
and being also specifically lighter than
the medium in which they move, must
suffer much greater resistance than the