Sacramento daily record-union. [volume] (Sacramento [Calif.]) 1875-1891, 1882-11-24
AFTERNOON SESSION.
THE MYSTERY OF COMETS TAILS.

The cometary displays of the last two
wears have excited in an unusual degree
the spirit of astronomical speculation as to
the causes of comets tails and their mys.
terious movements. An English scientist
in the October number Of the Philosophical
Magazine propounds novel theory to ex-
plain these phenomena. The forces on
which he relies to make out his theory are
the force of gravity which urges the comet
toward the sun, the expansive force of the
suns heat, and the resistance of an invisi.
BILE atmosphere surrounding the sun at i'm
mense distances. The changes in comet
which give rise to its tail begin with the
emission OF Jets of gas, in the direction de-
termined by the expansive force of the
suns heat acting on the comet. But soon
these Jets bend round, as if carried back
by strong wind, forming an envelope
round the body of the comet and
cone behind it, as would happen to man
dressed in loose robe and running rapidly
against the wind. The jets of gas escaping
from the body of the comet and expanding
when they leave it are more resisted by the
suns atmosphere than its more solid heat,
so that they seem to fall behind it, forming
the comets envelope and conical form be-
hind 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 leav-
ing each successive part thrown off more
and more behind it. After passing les peri
helion the comet carries its tail before it
instead of behind it, he says, because while
moving toward the sun it is perpetually
passing from rarer into denser medium,
while In recedipg from the sun it is perpet-
ually passing from a denser into rarer
medium. The fact that the most rapid
alteration in the direction of comets tails
necessarily occurs just when the expansive
| force of the suns heat is most felt
gives plausibility to this hypothesis
There can be little doubt that, as Mr..
Higgins observes, if we could see great
comet during its distant wanderlngs, when
it has put off the gala trappings OF peri
helion excitement, it would appear as a
very sober object, and consist of little more
thar nucleus alone" The game may per-
haps be said of the mysterious wanderer
while approaching the sun, but not near
enough to undergo vaporization from the
solar heat or to encounter the denser strata
OF the invisible solar atmosphere. The re-
cent inquiry of DR.. Siemens into the con-
servation of solar energy also lends color
to the theory that comets, when near the
sun, may encounter a resisting medium,
which would account for the phenomena IN
question as the writer referred to supposes.
But astronomers are yet far from solving
the old problems of thu origin and eccen-
trio behavior OF comets tails. There
seems to be" says Mr.. Higgins, &c a rapidly
growing feeling among physicists that both
the self-light of comets and the phenom-
ena of their tails belong to the order of
electric phenomena" This view, in order
to account for the carrying away of the
comets tail under an electrical repulsion
exerted by the sun, necessitates the suppo-
siticn that the sun is strongly electrified,
either positively or negatively, and also
that, in the changes going on in the comet,
the matter thrown off by the nucleus has
become strongly electrified in the same
way as the sun. Otherwise the attraction
on one side of every particle of the comet
would be precisely equal-as Herschel
points QUITO the repulsion on the oppo.
site side, and we should therefore be at a
loss to explain the enormous velocity with
which the matter of the tail is carried
backward, in opposition both to the motion
it had as part of the nucleus and to that it
acquired in the act of its emission. But
while all theories designed to explain
cometary phenomena have hitherto fallen
short of the mark, they have served to
stimulate accurate investigation, and also
to throw important light on the physics of
the sun and the diffusion OF matter in inter-
steller space.