The Jeffersonian. [volume] (Stroudsburg, Pa.) 1853-1911, 1858-10-21
NO, d..

motions Of the latter in the least pereep-
tble degree. BexelI's comet of 1870
dashed into the midst OF the system Of Ju
piter's satellites without at all affecting
their movements 4 curious calculation
is recorded of Sir Isaac Newton, that if q
globe of common atmospheric air, one
inch in diameter. we're expanded so as to
have an equal degree Of rarity with the
air situated at elevation Of 1000 miles
above the earth's surface, ''it void fill the
whole planetary regions as far as the
sphere of Saturn, and would extend
great deal further" Now, if this enoF-
mons extent of attenuated matter can be
conceived to be endowed with luminous
properties, whether from rejecting the
suns rays, or from its own Inherent phys
ical constitution, VIC can form proximatc-
ly, some sort of realizing sense or tho
nature of the magnificent feather which
now adorns the starry heavens. On this
point the speculations of philosophers are
interesting.
Before the time of the Tycho Braher
European observers had not ventured to
refer cometic aparitions to regions beyoDt
the moons orbit, aud and supposed them
indeed to be substances generated with
in the earth's atmosphere. The Danish
astronomer, however, from observations
upon the comet Of 1877, proved that these
bodies move in orbits beyond the earthS
satellite, and were therefore Of permanent
structure; and independent of the earth.
From observing that comet, as they e.
merge from the depths ofspaee, are moth
ing but mere specs of uebuiOslty, which ls
gradually prolonged into train as they
approach the sun, it was inferred that
comets are, in the normal condition,
spherical masses, like planets, aud that
to the sun. Some early observers sup
posed the tail was owing to the passage
of the suns rays through the nebulosity
of the head, producing an effect similar
to what is seen when beam OF the sun
pours through an aperture into dsrken-.
ed room. The Gartesian school referees
the effect to the refraction of light, in its
passage from the comet to the eye of the
observer, through the celestial ether dis
seminated through space. If this theory
be true, it has been Significantly asked,
why have the planets aud fixed stars no
tailsy Marion thought the effect procee-
ded from the same cause as that which
produces the aurora borealis.
The illustrious astronomer, Kepler,
who fourished early in the seventeeth
century, was the first to offer a rational
explanation Of this phenomenon. He
supposed that the constituent matter os
the comet is broken by the action Of the
solar rays, and the lighter PARTICLES in
PEELED to immense distances. Newton
conjectured that, as the nebulous parti-
ces Of the comet become heated by the
SUI, they communicate portion of their
heat to TIE contiguous particles of etheri-
al fluid composing the suns atmosphere.
These PARTICLES so heated (by reflection,
as it were), suffer correspo spondipg dimi-
mutton of density, and are repelled from
the sun, carrying with them the more
volatile particles of the cometary body,
just as an upward currant of air causes
smoke to ascend. But all hypothesis
must be vague where there are are so
few well-ascertained data. The great
discoveries made of late in electrical forces
promise to throw new light upon this pro-
louudly interesting subject.
The close approach Of some comets to
the sun in their perihelion passags, as for
example, in the case of the great comet
of lS43, before mentioned, and the i'm
mense distances to which they sometimes
recede from him in their aphelia, immeas-
urably beyond the utmost known limits
of our solar system, have led astronomers
to infer that comets are subjected, in the
course OF their orbital revolution, to al a
mazing degree of heat and cold.
Newton calculated that the comet of
1850 was subjected, at its perihtlion dis
tance of $50 900 miles, to a degree of
heat ? 600 times that of red hot iron!-
While, according to Hersehel, tue coUet
of ls43, which passed within 96, ,0GO
miles of tho sun, received, at its periheli
oD, an amount of heat equivalent to that
of Al 600 suns blazing in our skyl 1t
can scarcely be supposed that matter eau
U6 suUJecltu 10 SuCu O uC SsICS VI uSat WIN
out having its structure destroyed. La
place ayailed himself Of Black beautiful
discovery of latent heat to avoid this diff
! fculty, and taught that when body is
passing from liquid 20 a gaseous state,
it's particles, as they become suceessively
/ yolatlised, abstract from the body large
quantities OF caloric, and so serve to mod
crate the temperature of the eonden'ed
portion; aud, conversely, that this latent
calorio is given back by the volatlizcd
IN after In the course of its return to q
LIQUID state. So that comet, whether
swinging in its orbit few thousands of
miles from its local source Of heat and at
traction, or many thousands of millions
of miles distant, may preserve an aPTrox-
innate constancy Of oftemperatue uuder the
operation of this beautiful law ofeompeu-
sation.
Astronomers often differ widely in their
calculations Of comet upon lis first aP-