Comets and Meteors Part 8

The Meteors of April 30, May 1.

Professor Schiaparelli, in his list of meteoric showers whose radiant points are derived from observations made in Italy during the years 1868, 1869, and 1870, describes one as occurring on April 30 and May 1; the radiant being in the Northern Crown. The same shower has also been recognized by R. P. Greg, F.R.S., of Manchester, England. This meteor-stream, it is now proposed to show, is probably derived from one much more conspicuous in ancient times.

In Quetelet's "Physique du Globe" we find meteoric displays of the following dates. In each case the corresponding day for 1870 is also given,[28] in order to exhibit the close agreement of the epochs:

1. A.D. 401, April 9th; corresponding to April 29th, for 1870.

2. 538, " 6th; " April 25th, "

3. 839, " 17th; " May 1st, "

4. 927, " 17th; " April 30th, "

5. 934, " 18th; " May 1st, "

6. 1009, " 16th; " April 28th, "

[28] Making proper allowance for the precession of the equinoxes.

The epochs of 927 and 934 suggest as probable the short period of 7 years. It is found accordingly that the entire interval of 608 years--from 401 to 1009--is equal to 89 mean periods of 6.8315 years each. With this approximate value the six dates are all represented as follows:

From A.D. 401 to A.D. 538, 20 periods of 6.85 years.

538 to 839, 44 " 6.84 "

839 to 927, 13 " 6.77 "

927 to 934, 1 " 7.00 "

934 to 1009, 11 " 6.82 "

This period nearly corresponds to those of several comets whose aphelion distances are somewhat greater than the mean distance of Jupiter. So long as the cl.u.s.ter occupied but a small arc of the orbit the displays would evidently be separated by considerable intervals. The comparative paucity of meteors in modern times may be explained by the fact that the ring has been subject to frequent perturbations by Jupiter.

Groups in which the Meteoroids are spa.r.s.ely scattered.

By the labors of Heis, Greg, Herschel, Schiaparelli, and others, the radiants of more than fifty spa.r.s.ely strewn meteor-systems have been determined. Of these the following, which are well defined, seem worthy of special study:

DATE. POSITION OF RADIANT.

R. A. N. Decl.

January 1-4 234 51 January 18 232 36 April 25 142 53

The orbits and periods, except in the few cases previously considered, are entirely unknown. Some of the observed cl.u.s.ters are probably the _debris_ of ancient comets whose aphelia were in the vicinity of Jupiter's...o...b..t.

CHAPTER X.

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 s.p.a.ce, 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 ent.i.tled 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 ma.s.ses 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; ma.s.ses of matter, the volume of which is many hundred times greater than that of the earth, completely changing their position and form in the s.p.a.ce of a few minutes." The nature of this eruptive force is not understood. We may a.s.sume, 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 alt.i.tudes 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 r.e.t.a.r.ded 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. x.x.xii.

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 s.p.a.ces intervening between sidereal systems. Accordingly, the phenomena of comets and meteors have demonstrated the existence of such matter, widely diffused, in the portions of s.p.a.ce 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 ill.u.s.tration 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 cl.u.s.ters.

[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 quant.i.ties of hydrogen confined in the pores or cavities of certain meteoric ma.s.ses. 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 nebulae; 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.