Comets and Meteors Part 6

From 2 to 6 o'clock the numbers were so great as to defy all efforts at counting them; while their brilliancy was such that persons sleeping in rooms with uncurtained windows were aroused by their light. The meteors varied in apparent magnitude from the smallest visible points to fire-b.a.l.l.s equaling the moon in diameter. Occasionally one of the larger cla.s.s would separate into several parts, and in some instances a luminous train remained visible for three or four minutes. No sound whatever accompanied the display. It was noticed by many observers that all the meteors diverged from a point near the star _Gamma Leonis_; in other words, their paths if traced backward would intersect each other at a particular locality in the constellation Leo. In some parts of the country the inhabitants were completely terror-stricken by the magnificence of the display. In the afternoon of the day on which the shower occurred the writer met with an illiterate farmer who, after describing the phenomena as witnessed by himself, remarked that "the stars continued to fall till none were left," and added, "I am anxious to see how the heavens will appear this evening; I believe we shall see no more stars." A gentleman of South Carolina described the effect on the negroes of his plantation as follows:--"I was suddenly awakened by the most distressing cries that ever fell on my ears. Shrieks of horror and cries for mercy I could hear from most of the negroes of the three plantations, amounting in all to about 600 or 800. While earnestly listening for the cause I heard a faint voice near the door, calling my name. I arose, and, taking my sword, stood at the door. At this moment I heard the same voice still beseeching me to arise, and saying, 'O my G.o.d, the world is on fire!' I then opened the door, and it is difficult to say which excited me the most,--the awfulness of the scene, or the distressed cries of the negroes. Upwards of a hundred lay prostrate on the ground,--some speechless, and some with the bitterest cries, but with their hands raised, imploring G.o.d to save the world and them. The scene was truly awful; for never did rain fall much thicker than the meteors fell towards the earth; east, west, north, and south, it was the same."

At the time of this wonderful meteoric display Captain Hammond, of the ship _Rest.i.tution_, had just arrived at Salem, Ma.s.sachusetts, where he observed the phenomenon from midnight till daylight. He recollected with astonishment that precisely one year before, viz., on the 13th of November, 1832, he had observed a similar appearance (although the meteors were less numerous) at Mocha, in Arabia. It was found, moreover, as a further and most remarkable coincidence, that an extraordinary fall of meteors had been witnessed on the 12th of November, 1799. This was seen and described by Andrew Ellicott, Esq., who was then at sea near Cape Florida. It was also observed by Humboldt and Bonpland, in c.u.mana, South America. Baron Humboldt's description of the shower is as follows:--"From half after two, the most extraordinary luminous meteors were seen toward the east. Thousands of bolides and falling stars succeeded each other during four hours. They filled a s.p.a.ce in the sky extending from the true east 30 toward the north and south. In an amplitude of 60 the meteors were seen to rise above the horizon at E.N.E. and at E., describe arcs more or less extended, and fall toward the south, after having followed the direction of the meridian. Some of them attained a height of 40, and all exceeded 25 or 30. Mr. Bonpland relates, that from the beginning of the phenomenon there was not a s.p.a.ce in the firmament equal in extent to three diameters of the moon, that was not filled at every instant with bolides and falling stars. The Guaiqueries in the Indian suburb came out and a.s.serted that the firework had begun at one o'clock. The phenomenon ceased by degrees after four o'clock, and the bolides and falling stars became less frequent; but we still distinguished some toward the northeast a quarter of an hour after sunrise."

This wonderful correspondence of dates excited a very lively interest throughout the scientific world. It was inferred that a recurrence of the phenomenon might be expected, and accordingly arrangements were made for systematic observations on the 12th, 13th, and 14th of November. The periodicity of the shower was thus, in a very short time, placed wholly beyond question. The facts in regard to the phenomena of November 13, 1833, were collected and discussed by Olmsted, Twining, and other astronomers. The inquiry, however, very naturally arose whether any trace of the same meteoric group could be found in ancient times. To determine this question many old historical records were ransacked by the indefatigable scientist, Edward C. Herrick, in our own country, and by Arago, Quetelet, and others, in Europe. These examinations led to the discovery of ten undoubted returns of the November shower previous to that of 1799. The descriptions of these former meteoric falls are given by Professor H. A. Newton in the _American Journal of Science_, for May, 1864. They occurred in the years 902, 931, 934, 1002, 1101, 1202, 1366, 1533, 1602, and 1698. Historians represent the meteors of A.D. 902 as innumerable, and as moving like rain in all directions. The exhibition of 1202 was scarcely less magnificent. "On the last day of Muharrem,"

says a writer of that period, "stars shot hither and thither in the heavens, eastward and westward, and flew against one another like a scattering swarm of locusts, to the right and left; this phenomenon lasted until daybreak; people were thrown into consternation, and cried to G.o.d the Most High with confused clamor." The shower of 1366 is thus described in a Portuguese chronicle, quoted by Humboldt: "In the year 1366, twenty-two days of the month of October being past, three months before the death of the king, Don Pedro (of Portugal), there was in the heavens a movement of stars such as men never before saw or heard of. At midnight, and for some time after, all the stars moved from the east to the west; and after being collected together, they began to move, some in one direction and others in another. And afterward they fell from the sky in such numbers, and so thickly together, that as they descended low in the air they seemed large and fiery, and the sky and the air seemed to be in flames, and even the earth appeared as if ready to take fire.

That portion of the sky where there were no stars seemed to be divided into many parts, and this lasted for a long time."

The Showers of 1866-9.

The fact that all great displays of the November meteors have taken place at intervals of 33 or 34 years, or some multiple of that period, had led to a general expectation of a brilliant shower in 1866. In this country, however, the public curiosity was much disappointed.[22] The numbers seen were greater than on ordinary nights, but not such as would have attracted any special attention. The greatest number recorded at any one station was seen at New Haven by Professor Newton. On the night of the 12th 694 were counted in five hours and twenty minutes, and on the following night, 881 in five hours. A more brilliant display was, however, witnessed in Europe. Meteors began to appear in unusual frequency about 11 o'clock on the night of the 13th, and their numbers continued to increase with great rapidity for more than two hours; the maximum being reached a little after 1 o'clock. A writer in Edinburgh, Scotland, thus describes the phenomenon as observed at that city:--"Standing on the Calton Hill, and looking westward,--with the observatory shutting out the lights of Princes Street,--it was easy for the eye to delude the imagination into fancying some distant enemy bombarding Edinburgh Castle from long range; and the occasional cessation of the shower for a few seconds, only to break out again with more numerous and more brilliant drops of fire, served to countenance this fancy. Again, turning eastward, it was possible now and then to catch broken glimpses of the train of one of the meteors through the grim dark pillars of that ruin of most successful manufacture, the National Monument; and in fact from no point in or out of the city was it possible to watch the strange rain of stars, pervading as it did all points of the heavens, without pleased interest and a kindling of the imagination, and often a touch of deeper feeling that bordered on awe."

At London about 1 o'clock a single observer counted 200 in two minutes.

The whole number seen at Greenwich was 8485. The shower was also observed in different countries on the continent.

[22] The first indication of the approaching shower was the appearance of meteors in unusual numbers at Malta, on the 13th of November, 1864. In 1865, as observed at Greenwich and other stations, they were still more numerous.

In 1867 the display was generally observed throughout the United States.

From the able and interesting reports of Commodore Sands and Professors Newcomb, Harkness, and Eastman, we derive the following facts in regard to the shower as seen at Washington, D. C.:

Commencement 1_h._ 0_m._ A.M. Nov. 14.

Maximum 4 20 " "

End 5 0 " "

Number of meteors per hour at maximum 3000 Mean height on first appearance 75 miles.

" " on disappearance 55 "

Position of radiant, R. A. 151, Decl. 22-1/2.

The shower of 1868 was in some respects quite remarkable, though the number of meteors was less than in 1866 or 1867. At New Haven the fall commenced about midnight, and from 2 o'clock till daybreak over 5000 meteors were counted. The time of maximum could not be accurately determined, as no decrease in the numbers was observable till dawn. The display was also witnessed in England and in Cape Colony, South Africa.

The times of maxima in these countries differed so materially as to indicate a decided stratification of the meteoric stream. The entire depth, moreover, where crossed by the earth in 1868, was much greater than at the part traversed either in 1866 or 1867.

In 1869 the shower was observed at Port Sad, Lower Egypt, by G. L.

Tupman, Esq.; in Florida, U. S., by Commander William Gibson, U.S.N.; and at Santa Barbara, California, by Mr. G. Davidson and Mrs. E.

Davidson. The first observed 112 meteors in 1h. 54m., from 2h. 30m. to 4h. 24m., Alexandria mean time; the numbers during this interval being nearly equal, though slightly decreasing. Throughout the morning (November 14) the sky was only partly clear. The two observers at Santa Barbara saw 556 in 2h. 25m., ending at 3h. 43m. A.M. In Florida also the display was quite brilliant, though inferior to that of 1868. It should be remarked that the morning in many parts of the United States was cloudy. No considerable number of the meteors of this stream has been observed in any part of the world since 1869.

DISCUSSION OF THE PHENOMENA.

Since the memorable display of November 13, 1833, the phenomena of shooting-stars have been observed and discussed with a very lively interest. Among the first laborers in this department of research the names of Olmsted, Herrick, and Twining must ever hold a conspicuous place. The fact that the position of the radiant point did not change with the earth's rotation at once placed the cosmical origin of the meteors wholly beyond question. The theory of a ring of nebulous matter revolving round the sun in an elliptic orbit--a theory somewhat different from that proposed by Olmsted--was found to afford a simple and satisfactory explanation of the phenomena. This hypothesis of an eccentric stream of meteors intersecting the earth's...o...b..t was adopted by Humboldt, Arago, and others, shortly after the occurrence of the meteoric shower of 1833.

A few years previous to the display of 1866 it was shown by Professor Newton, of Yale College, that the distribution of meteoric matter around the ring or orbit is far from uniform; that the motion is retrograde; that the node of the orbit has an annual forward motion of 102".6 with respect to the equinox, or of 52".4 with respect to the fixed stars; that the periodic time must be limited to five accurately determined periods, viz.: 180.05 days, 185.54 days, 354.62 days, 376.5 days, or 33.25 years; and that the inclination of the orbit to the ecliptic is about 17. Professor Newton, for reasons a.s.signed, regarded the third period named as the most probable. He remarked, however, that by computing the secular motion of the node for each periodic time, and comparing the result with the known precession, it was possible to determine which of the five periods is the correct one.

For the application of this crucial test,--a problem of more than ordinary interest,--we are indebted to Professor J. C. Adams, of Cambridge, England. By an elegant a.n.a.lysis it was first shown that for either of the first four periods designated by Professor Newton, the annual motion of the node, resulting from planetary perturbation, would be considerably less than one half of the observed motion. It only remained, therefore, to examine whether the period of 33-1/4 years would give a motion of the node corresponding with observation. Professor Adams found that in this time the longitude of the node is increased 20'

by the action of Jupiter, 7' by the action of Saturn, and 1' by that of Ura.n.u.s. The effect of the other planets is scarcely perceptible. The _calculated_ motion in 33-1/4 years is therefore 28'. The _observed_ motion in the same time, according to Professor Newton, as previously stated, is 29'. This remarkable accordance was at once accepted by astronomers as satisfactory evidence that the period is about 33.25 years.

Having determined the periodic time, the mean distance, or semi-axis major, is found by Kepler's third law to be 10.34. The aphelion is consequently situated at a comparatively short distance beyond the orbit of Ura.n.u.s. The orbit is represented in Fig. 4.

[Ill.u.s.tration: Fig. 4.]

It was stated at the close of Chapter VI. that shooting-stars are the dissevered fragments of cometic matter, which, penetrating our atmosphere, are rendered luminous by the resistance so encountered. The discovery that comets and meteors are actually moving in the same orbits was first announced by Signor Schiaparelli in 1867. The coincidence of the orbits of Tempel's comet[23] as computed by Dr. Oppolzer, and the meteors of November 14 as determined by Schiaparelli, is too close to be regarded as merely accidental. These elements are as follows:

Nov. Meteors. Tempel's Comet.

Perihelion pa.s.sage Nov. 10.092, 1866. Jan. 11.160, 1866.

Pa.s.sage of descending node Nov. 13.576, Longitude of perihelion 56 26' 60 28'

Longitude of ascending node 231 28' 231 26'

Inclination 17 44' 17 18'

Perihelion distance 0.9873 0.9765 Eccentricity 0.9046 0.9054 Semi-major axis 10.3400 10.3240 Periodic time 33.2500 _y._ 33.1760 _y._ Motion Retrograde. Retrograde.

[23] See page 30.

The fact is thus obvious that the meteors of November 14 are the products of the comet's gradual dissolution. It has been stated that the comets of 1366 and 1866 are probably identical. The interval indicates a period of 33.283 years--greater by 39 days than that found by Oppolzer.

With this value of the periodic time and the known secular variation of the node it is found that the comet and Ura.n.u.s were in close proximity about the beginning of the year 547 B.C. It is therefore not improbable that the former was then thrown into its present orbit by the attraction of the latter. The celebrated Leverrier designated the year 126 of our era as the probable epoch of the comet's entrance into our system. This date, however, is incompatible with the period here adopted. It is worthy of remark, moreover, as bearing on this question, that the extension of the cl.u.s.ter in the tenth century, as indicated by the showers of 902, 931, and 934, was too great to have been effected in so short a period as 800 years.

With the period of 33.283 years it is easy to find that the comet will make a near approach to the earth about the 16th or 17th of November, 1965, and to Ura.n.u.s in 1983. At one of these epochs the cometary orbit will probably undergo considerable transformation.

We have seen that the comet of 1866, and also the meteoroids following in its path, have their perihelion at the orbit of the earth, and their aphelion at the orbit of Ura.n.u.s. Both planets, therefore, at each encounter with the current not only appropriate a portion of the meteoric matter, but entirely change the orbits of many meteoroids. In regard to the devastation produced by the earth in pa.s.sing through the cl.u.s.ter, it is sufficient to state that, according to Weiss, the meteor orbits resulting from the disturbance will have all possible periods from 21 months to 390 years. It may be regarded, therefore, as evidence of the recent[24] introduction of this meteor-stream into the solar system that the comet of 1866, which const.i.tutes a part of the cl.u.s.ter, has not been deflected from the meteoric orbit by either the earth or Ura.n.u.s.

[24] Recent in comparison with the origin of the August meteors, which const.i.tute a continuous ring.

CHAPTER IX.

OTHER METEORIC STREAMS.

_The Meteors of August 7-11._--Muschenbroek, in his "Introduction to Natural Philosophy," published in 1762, stated as the result of his own observations that shooting-stars are more abundant in August than in any other part of the year. The fact, however, that a maximum occurs on the 9th or 10th of the month was first shown by Quetelet in 1835. Since that time the shower has been regularly observed both in Europe and America; the number of meteors at the maximum sometimes amounting to 160 per hour. Their tracks when produced backward intersect each other at a particular point in the constellation Perseus.

Of the 315 meteoric displays given in Quetelet's catalogue, 63 belong to the August epoch. Their dates up to the commencement of the present century are as follows:

1. A.D. 811, July 25th.

2. 820, " 25th-30th.

3. 824, " 26th-28th.

4. 830, " 26th.

5. 833, " 27th.

6. 835, " 26th.

7. 841, " 25th-30th.

8. 924, " 27th-30th.

9. 925, " 27th-30th.

10. 926, " 27th-30th.

11. 933, " 25th-30th.

12. 1243, Aug. 2d.

13. 1451, " 7th.

14. 1709, " 8th.

15. 1779, " 9th-10th.

16. 1781, " 8th.

17. 1784, " 6th-9th.

18. 1789, " 10th.

19. 1798, " 9th.

20. 1799, " 9th-10th.