Public ledger. [volume] (Memphis, Tenn.) 1865-1893, 1883-06-22
The Mystery Of Comets, rails,

SS'0Ey OA NOmctp TAILS
The cometary displays of the Ia.
two years have excited in an unusu;
degree the spirit of astronomical spec
ulation as to the causes of comet,
tails and their mysterious movement
An English scientist in the Philosc
phlcal Magazine propounds a nov,
theory to explsin these phenomen,
The forces on which he relies to max
out his theory are the force of grayit
which urges the comet toward th
sun, the expansive force of the sun
heat, and the resistance Of an invisi
Bile atmosphere surrounding the su
at immense distances. The change
in comet which give rise TO its tai
begin with the emission of ga
in the direction determine,
by the expansive force o
the suns heat acting on tn
comet. But soon these lets benz
round, as if carried back By a strouI
wind, forming an envelope round the
body OF the comet and a cone behinC
it, as would happen to a man dressed
in 3 loose robe and running rapidl,
against the wind, The lets Of gas es
Gaping from the body OF the comet anC
expanding when they leave it are more
resisted by the suns atmosphere thar
its more solid heat, SO that they seen
to fall behind it. forming the comets
envelope 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 a tail
by leaving each successive part thrown
off more and more behind it. After
passing its perihelion the comet carrie:
It's 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
receding from the sun it is perpetually
passing from a denser into a rarer
medium.
The fact that the most rapid altera
ton in the direction of comets tails
necessarily occurs just when the ex.
pansive force Of the suo' heat is most
felt gives plausibility to this hypothe-
sis. There can be little doubt that,
as Mr.. Higgins observes: IF we
could see a great comet during its
distant wanderings, 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 than nucleus alone" The
same may perhaps he said of the
mysterious wanderer while approach
ing the sun, but not near enough to
undergo vapOrizatiOn froi1 the solar
heat or encounter the denser strata OF
the invisible solar atmosphere. The
recent inquiry of Du Sismens into the
conservation of solar energy also lends
color to the theory that comets when
near the sun may encounter a resist
ing medium, which would account
for the phenomena in question, as
the writer referred to supposes.
But astronomers are yet far from
solving the problems of the origin
and eccentric behavior Of com.
cts 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 electric phenomena"
This few, in order to account for the
carrying away Of the comets tail un
der an electric repulsion exerted by
the sun, necessitates the supposition
that the sun is strongly electrified
either positively or negatively, and
also that the changes going on in the
comet, the matter thrown of by the
nucleus has become strongly eleo-
tri6ed 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 repul,
sion on its opposite side, and we
should therefore be at loss to explain
the enormous velocity with which
the matter of the tail is carried backs
ward, in opposition both to the motion
it had as part of the nucleus and TO
that it acquired in the act of its ar,iis
sion. But while all theories designed
to explain cometary phenomena have
hitherto fallen short OF the mark, they
have served to stimulate active inyes,
tigation, aud also to throw important
light on the physics of the sun and the
diffusion OF matter in intersteller
space.