Bristol news. [volume] (Bristol, Va. & Tenn.) 1867-189?, 1874-07-21

certainly affirmed that they visit us
but once. These comets like the
periodic comets can be seen only
when in that short part of their orbits
which is near the sun and earth.
Unlike the periodic comets their ar
rival cannot be predicted, as eclipses
and tranSitS can.
KEPLER said comets were as plenty
as fish in the ocean. ARAGo calcu-
lated that within the orbit of Neptune
there were 1880. HRRscuEL
reckoned the number of those visi-
ble by the help of the telescope at
25. 900. Of the 200 recorded, and
the 600 noted in ancient annals, only
about 40 have had their periods of
revolution determined.
Some comets are the largest objects
IN the solar system, surprising even
the sun in volume. The comet of
1911. which will return when the
Capitol at Washington is as old as
the Pyramids of Egypt. measured at
the diameter of its luminous nucleus
more than 400 miles, the diameter of
its coma $4,000 miles. the length of
its tail 112 900 900 miles. Yet the
hngeSt of them all is perhaps out
weighed many thousandfold by the
tiniest asteroid.
The substance Of comets is mat
ter, for although comets are self
luminous objects portion of the
light we receive from them is reflected
solar light. Under proper conditions
its polarization betrays this fact Of
their constitution But the matter
of comets must be of infinite tenuty.
A Whit of cigar smoke at night
will block for an instant the light Of
the brightest planet. a puff from
locomotive will blot out the daz-
zling beam of the sun on its way to
the eye, But the light of Arcturus
has passed through 0,C00 lriles of
a comets tail to an astronomers eye
unhludered, and comets Lave been
seen to pass between us and nebuln
of excessive faintness without di-
miniShing their light. Again TIE
comet of 1770 became entangled
among the satellites of Jupiter, yet
had no perceptib'e influence upon
their motions or times.
Of observed comets only the more
brilliant display long tails. DoNATI's
comet of 1858 was one of the finest.
Sir JOHN MERsCHEL in his essay upon
comets grew eloquent upon that
superb aigrette form, like
tall plume waited by the breeze"
1t IS the general fact that the tails
of comets, whether approaching,
rounding or leaving the sun, tend
from the sun. though rarely if ever
exactly in the direction of line from
the sun through tie head of comet.
Nearly all comets show as they near
the sun a lengthening of their figure
corresponding to the change which |
in the case larger comets precedes |
the formation o: tail. 1t is not |
everywhere the same tail, but, to use
HERsCHEL's expression, "fresh mat
ter continually streaming forth"
These facts which we have recited, |
others which are equally known to
aud still other justly
from the known laws of
motion, and force, have not
yet been combined into a consistent
cOmetic theory. 1t is hoped that
spectroscopic analysis, which, being
of so recent date, has thus far been
applied almost alone to telescope
comets, will now or soon disclose
enough n ore facts to lay the basis of
a sound theory. Sir JOHN HERsCHEL
thought it "demontrated" that "the
tail of "a comet is neither more nor
less than the accumulation of sort
of luminous vapor darted soft in the
first Instance towards the sun. as if
"it were something raised up, and as
it were exploded by the suns heat.
out of the kernel. ''and then i'm
and forcibly turned ''back
and repelled from the SUM-"
The observed association between
meteors and comets is reconciIable
with this theory, and indeed HERcHEL
expressly stated the case of this
replusive force. mightier than the
attractive power of the sun, driving
off irrecoverably portions of the tail
remote from the nucleus. Professor
TYNDALL. subjecting the ut:mate
PARTICLES of matter 30 analysis in his
laboratory by the action of ethereal
waves, has ''shaken asunder the
molecules of vapor" and brought
down upon bis light-beam shower of
liquid particles which revealed its
presence and form. So he would
nave us look on comet as composed
1f a vapor which the suns light is
able to decompose, cloud formed by
md revealing the presence of his
lctinic beams.
The spectroscope in DR.. HUGGINs's
,ands has already disclosed that the
nucleus of a comet consists of self
luminous gas. in every case heretofore
observed. WINNECKE's comet Of
1868, which is soon due again we be-
ieve, was discovered to consist of the
luminous vapor of carbon. The
coma which is the faint light around
he nucleus is found on the othe hand
o shine in part by reflected solar
ight. What the tails of comets are
n this respect PRoCToR said as late
5 two years ago. 1--WE have as yet
earned nothing" But CoGGIA's
omes is nightly undergoing the
losest inspection at the hands of
cores of spectroscopists and we shall
cry speedily learn form them the ma
lre of all its parts. Already the |
stronomer of the famous Paris i
Professor RAYET, re- t
,icing 10 be Of the first tn apply, in
he case Of brilliant comet visible
} the naked eve, the spetroscOpe to q