fr:Hector Servadac - II - Chapitre III
CHAPTER III.COMETS, OLD AND NEW.
As if moved by some unconscious presentiment of his
future destiny, Professor Palmyrin Rosette had always
evidenced a strong predilection for the study of comets. He had based his opinions on the best authorities, and was never more in his element than when he was expatiating on his favourite theme as he presided at some astronomical conference.
“Comets, gentlemen,” he would say, “are nebulous
bodies which occasionally appear in the heavens, consisting
ordinarily of a bright central light called the nucleus and
in the more conspicuous cases accompanied by a long trail
of light called the tail. Owing to the great eccentricity of
their orbits, they are visible to the earth during only a
portion of their course.”
The professor never failed to point out the two characteristics
by which they were to be distinguished from other
heavenly bodies:
“Although these comets, gentlemen, may be deficient
either with respect to the luminous tail or to the nebulous
coma, the progressive motion with which they are endued
prevents them from ever being mistaken for fixed stars, while the extreme length of the ellipses which they describe makes it impossible to confound them with planets,”
During the long years of the astronomer's application
to his fascinating study, he had composed an elaborate
treatise, exhibiting the results of all his investigations, and
when, after the sudden convulsion, he found himself
actually upon the surface of one of the very bodies the
properties of which had engrossed so much of his interest, it was necessarily a disappointment to feel that, alone upon Formentera, he had no audience to whom he could address himself.
The treatise which Rosette had compiled had been
arranged under four distinct heads:
1. The number of comets.
2. Periodic and non-periodic comets.
3. The probability of collision between a comet and
the earth.
4. The consequences of such a collision.
First: with respect to the number of comets, the
professor had recorded that, according to Arago, who
grounded his estimate on the number that revolve between
Mercury and the sun, there are at least 17,000,000 of these
luminous bodies in our solar system; whilst Lambert asserts
that within the orbit of Saturn, that is, within a radius of
872,135,000 miles, there are no less then 500,000,000. According to Kepler, two hundred years previously, the number of comets can only be compared to the fishes in the sea, and in following out his simile he declares that an angler throwing out his line from the surface of the sun could not fail to touch several of them; and now in recent times a computation has been made that their aggregate reaches a total of 74,000,000,000 distinct comets. The truth seems to be that their number really sets all calculation at defiance; so erratic, moreover, are their movements, that they sometimes pass from system to system, and whilst some, entirely escaping the influence of the sun, vanish, to find a new centre of attraction, others never before observed make their appearance upon the terrestrial horizon.
Even the comets which belong exclusively to our own
system are by no means exempt from strange irregularities; the orbits of several, ceasing to be ellipses, have become
parabolas or hyperbolas; and the planets, Jupiter in particular, have been observed to exercise a large disturbing action upon their paths.
Secondly: under the head of periodic and non-periodic
comets, Professor Rosette had stated that as many as 500
or 600 comets have been made objects of careful astronomical
investigation; those being called “periodic” of which
the return at fixed intervals has been established as a
certainty; those, on the other hand, being classed as “non-periodic” which recede to such immeasurable distances from the sun that it cannot be determined whether they will return or not.
Of the periodic comets there are not more than forty
of which the times of their revolution have been ascertained
with exact precision; but of these there are ten, generally
known as the “short-period comets,” the movements of
which have been established with the nicest accuracy.
