THE ORIGIN OF COMETS AND METEORS.
The fact that comets and meteors, or at least a large proportion of such
bodies, have entered the solar system from stellar space, is now
admitted by all astronomers. The question, however, in regard to the
origin and nature of these cosmical clouds still remains undecided. The
theory that they consist of matter expelled with great velocity from the
fixed stars appears to harmonize the greatest number of facts, and is
accordingly entitled to respectful consideration. The evidence by which
it is sustained may be briefly stated as follows:
1. The observations of Zollner, Respighi, and others, have indicated the
operation of stupendous eruptive forces beneath the solar surface. The
rose-colored prominences, which Janssen and Lockyer have shown to be
masses of incandescent hydrogen, are regarded by Professor Respighi as
phenomena of eruption. "They are the seat of movements of which no
terrestrial phenomenon can afford any idea; masses of matter, the volume
of which is many hundred times greater than that of the earth,
completely changing their position and form in the space of a few
minutes." The nature of this eruptive force is not understood. We may
assume, however, that it was in active operation long before the sun
had contracted to its present dimensions.
2. With an initial velocity of projection equal to 380 miles per second,
the matter thrown off from the sun would be carried beyond the limits of
the solar system, never to return. With velocities somewhat less, it
would be transported to distances corresponding to those of the aphelia
of the periodic comets.
3. On the 7th of September, 1871, Professor Young, of Dartmouth
College,[29] witnessed an extraordinary explosion on the sun's surface.
The observer, with his telescope, followed the expelled matter to an
elevation of over 200,000 miles. The mean velocity between the altitudes
of 100,000 and 200,000 miles was 166 miles per second. This rate of
motion _in vacuo_ would indicate an initial velocity of about 260 miles
per second. But the sun is surrounded by an extensive atmosphere, whose
resistance must have greatly retarded the velocity of the outrush before
reaching the height of 100,000 miles. The original velocity of these
hydrogen clouds was therefore sufficient, in all probability, to have
carried them, if unresisted, beyond the solar domain. Solid or dense
matter propelled with equal force would doubtless have been driven off
never to return.[30]
[29] Boston Journal of Chemistry, November, 1871.
[30] See Mr. Proctor's interesting discussion of this subject in
the Monthly Notices of the R.A.S., vol. xxxii.
4. This eruptive force, whatever be its nature, is probably common to
the sun and the so-called fixed stars. If so, the dispersed fragments
of ejected matter ought to be found in the spaces intervening between
sidereal systems. Accordingly, the phenomena of comets and meteors have
demonstrated the existence of such matter, widely diffused, in the
portions of space through which the solar system is moving.
5. According to Mr. Sorby the microscopic structure of the aerolites he
has examined points evidently to the fact that they have been at one
time in a state of fusion from intense heat,--a fact in striking harmony
with this theory of their origin.
6. The velocity with which some meteoric bodies have entered the
atmosphere has been greater than that which would have been acquired by
simply falling toward the sun from any distance, however great. On the
theory of their sidereal origin, this excess of velocity has been
dependent on the primitive force of expulsion. The shower of aerolites
which fell at Pultusk, Poland, on the 30th of January, 1868,[31] is not
only a remarkable illustration of the fact here stated, but also of
another which may be accounted for by the same theory, viz.: that
meteoric bodies sometimes enter the solar system in groups or clusters.
[31] See Chapter VII.
7. A striking argument in favor of this theory may be derived from the
researches of the late Professor Graham, considered in connection with
those of Dr. Huggins and other eminent spectroscopists. Professor Graham
found large quantities of hydrogen confined in the pores or cavities of
certain meteoric masses. Now, the spectroscope has shown that the sun's
rose-colored prominences consist of immense volumes of incandescent
hydrogen; that the same element exists in great abundance in many of the
fixed stars, and even in certain nebulæ; and that the star in the
Northern Crown, whose sudden outburst in 1866 so astonished the
scientific world, afforded decided indications of its presence.
THE END.
_BY THE AUTHOR OF THIS VOLUME._
METEORIC ASTRONOMY:
A TREATISE ON
SHOOTING STARS, FIRE BALLS,
AND AEROLITES.
BY DANIEL KIRKWOOD, LL.D.
12mo. Extra Cloth. $1.50.
For sale by Booksellers generally, or will be sent by mail,
postpaid, on receipt of the price by
J. B. LIPPINCOTT & CO., Publishers,
_715 and 717 Market St., Philadelphia_.
Transcriber's Note: Obvious errors in spelling and punctuation have been
corrected. Footnotes have been renumbered and moved from the page end to
the end of the paragraph. Images have been moved from the
middle of a paragraph to the closest paragraph break.