The Savannah morning news., 1903-08-30

More volatile material is doubtless
mixed up with this, inasmuch as the
tail of a comet appears only when the
mead approaches the sun. Another phe-
nomenon which suggests that solar
warmth is the immediate cause of that
development is that the luminous train
seems to be shot out from the front
OF the nucleus. or the side nearest the
sun: On occasions short fanlike pro-
Jectlons continue to point in shat d.
rectlon, but the tail proper quickly
falls backward. This is its position so
long as the comet is coming in toward
the sun. AS soon as the nucleus has
begun TO recede the tail goes ahead.
TOT that remdrka BILE behavior no bet
Ter explanation has yet been offered
imam that the sun exercises an electri-
cal repulsion. When that theory was
advanced seventy-odd years ago by Oh
oers II made only little impression on
other astronomers. but faith in it has
steadily increased ever since. OF
course If interstellar space was filed
With air the performance which is wit
messed at perihelion would be attended
with immense difficulty. There, inside
OF Two or three days, perhaps, the head
OF the comet swings around an arc of
nearly $50 degrees, and In order 10
maintain its normal attitude the tail
must make a tremendous sweep in d
very snort time. If, as was the case
with the comet of 1858, the tail was
over 5O,000000 miles long, and if the
medium in which it moved offered any
resistance to that maneuver. the tail
would probably be sadly denoralized
us own average density is estimated
70 De lower than that of fog. AS it is,
the appendage goes around with the
precision of a platoon of regulars ex-
ecuting a right wheel.
Brediknine, who was SUCCESSFULLY
director of the Moscow and Pulkowa
obserVatories, made a provisional clas-
sl1cation of comets in accordance with
the form of their tails. If the latter
were exceedingly straight, he computed
mat the repellent force of the sun was
sixteen times greater than its attrac-
ton. Where the appendage was curry
ed, ike scimetar of plume, the excess
was much lower, though it was ade-
quate Che thought) to give the elected
matter velocity of a mile a second.
Bredikhine's third type included COM
cts whose tails were short and brush
like, and which had two or three tails,
He believed that the repellent force
might not here be more than from 10
to 30 per cent. greater than gravity.
The Russian suggested that these
dlssimilarities might be due to differ
ences in the composition of the tails.
He fancied that the long straight ones
might consist of almost pure hydrogen.
the curved ones of hydrocarbons dixie
Illuminating gas) and that the third
might contain iron vapor. The spec
troscope does not reveal any pure hy-
drogen tails, and there is doubt about
the presence of iron, too, in the train,
thought it undoubtedly exists in many
nuclei. This later theory of Bredik-
hine, therefore, is not generally accep-
ted. Miss Clerke says, ELECTRICITY
alone seems competent to produce the
varieties of cometary emanation'
though she does not indicate just how.
Even the novice in astronomy has
noticed the resemblance between the
attenuated nebulous envelope of the
sun, known as the corona, and the
gauzy texture Of a comets tail A
striking illustration of the delicacy of
the former was afforded in 1882, when a
comet passed within 100000 miles of
the solid surface. This distance is
about one-third of a solar diameter.
Hence the comet was not immersed in
the corona. Neither the speed of the
vagrant nor the form of it's appen-
dage was perceptibly affected by the
encounter, though the retarding effect
which might have been anticipated
lasted through at least half a million
miles of the Journey