San Marcos free press. [volume] (San Marcos, Tex.) 1877-1892, 1883-01-11
COMETS TAILS.


i nc COutthIy uibpiuy vi tno ldbt
two years have excited in an unusual
degree the spirits of astronomical
speculation as to the causes of
comets tails and their mysterious
movements. An English scientist in
the Philosophical Magasine propounds
a novel theory to explain these phe-
uomena. The forceson which he re-
lies to make out his theory are the
forces of gravity which urgethe comet
toward the sun, the expansive force
of the suns heat, and the resistance
of an invisible atmosphere surround
ing the sun at immense distances.
The changes in a comet which give
rise to it's tail begin with the emission
of Jets of gas, on the direction de-
termined by the expansive force Of the
suns heat acting On the comet. But
soon these jets bend round, as if car
ried back by a STRONG wind,s forming
an envelope round the body Of the
comet and a cone behind it, as would
happen to, man dressed in a loose
robe and running rapidly against the
wind, The Jets of gas escaping from
the body of the comet understanding
when7t they leave it are more resisted
by the sun s atmosphere thanits more
solid heat, SO that they seem to fall
behind it, forming the comets enyel.
ope and conical form behind the head.
According to this view the body of the
comet is constantly moving through
the vapors it throws off, and thus
produces the appearance Of tail by
leaving each successive part thrown
off more and more behind it. After
passing its perihelion the comet car
ries it's tail before itinstead of behind
it, he says, because while, moving to-
ward the sun tits perpetually pass
ing from q rarer into d densermedium,
while in receding from, the SUN it is
perpetrally passing from q denser in
to rarer medium. g.. isisA
The fact that the most rapid altera-
ton in the direction Of comets tails
necessarily occurred when the expan-
.sive force of the suns heat is most
felt gives plausibility to this hypothe-
sis. There can be little doubt that,
as Mr.. Higgins observes, IF we
could see great comet during its
distant wanderings, when it has put
off the gala trappings of perihelion
excitement, it would appear as a very
sober object, and consist of little
more than nucleus alone" The same
may perhaps be said Of themystereus
wanderer while approaching the sun
but not near enough to undergo vap,
orization from the solar heat or to
encounter the denser strata of the
invisible solar atmosphere. The re-
cent inquiry Of DR.. Siemens into the
conservation of solar energy also
lends color into the theory that COM
cts when near the sun may encoun-
ter resisting medium, which would
account for the phenomena in ques-
ton as the writer referred to supposes.
But astronomers are yet far from
solving the old problems of the origin
and eccentric behavior of comets
tails. "There seems to be-" says Mr..
Higgins, a rapidly growing feeling
among physicists that both the self
light of comets and the phenomena OF
their tails belong to the order of cleo
trio phenomena. This view, in order
to account for the carrying away OF
the comets tail under an electric re-
pulsion exerted by the sun, necessi-
tates the supposition that the sun is
strongly electrified, either positively o,
negatively, and also that, in the
changes going OH in the comet, the
matter thrown off by the nucleus has
become strongly electrifiedin the same
way as the sun. Otherwise the at
traction on one side of every particle
of the comet would be precisely equaI
AS Herschel points QUITO the re-
pulsion on it's opposite side, and we
should therefore be at loss to ex
plain the enormous velocity with
which the matter of the tail is car.
ried backward, in opposition both tc
the motion it has as part of the nu'
cleus and to that it acquired in the
act of its emission. But while al
theories designed to explain cometary
phenomena have hitherto fallen short
of the mark, they have served to stun
ulate accurate investigation, and also
to throwimportantlig hton the physics
of the sun and the diffusion of matter
in interstellar space.