The views of Dr. Weiss, of Vienna, differ from those of Schiaparelli, in that he regards comets as the original bodies by whose disintegration meteor-streams are gradually formed.[26] "Cosmical clouds," he remarks, "undoubtedly appear in the universe, but only of such density that in most cases they possess sufficient coherence to withstand the destructive operation of the sun's attraction, not only up to the boundaries of our solar system, but even within it. Such cosmical clouds will always appear to us as comets when they pass near enough to the earth to become visible. Approaching the sun, the comet undergoes great physical changes, which finally affect the stability of its structure: it can no longer hold together: parts of it take independent orbits around the sun, having great resemblance to the orbit of the parent comet. With periodical comets, this process is repeated at each successive approach to the sun. Gradually the products of disintegration are distributed along the comet's orbit, and if the earth's orbit cuts this, the phenomenon of shooting-stars is produced."
These views of the distinguished astronomer of Vienna are confirmed by the star-shower of November 27, 1872. That the orbits of the earth and Biela's comet intersect at the point passed by the former about the last of November, and that in 1845 the comet separated into two visible parts, has been stated in a previous chapter. The comet's non-appearance in December, 1865, and in September, 1872, was regarded by astronomers as presumptive evidence of its progressive dissolution. A meteoric shower, resulting from the earth's collision with the cometary débris, was accordingly expected about the 27th of November.
The first indication of the approaching display appeared on the evening of November 24, when meteors in unusual numbers were observed by Professor Newton, at New Haven, Connecticut. On Wednesday evening, the 27th, from the close of twilight till 8 o'clock, a decided shower of shooting-stars was noticed in various parts of the United States. At Greencastle, Indiana, Professor Joseph Tingley counted 110 meteors in 40 minutes, and at Princeton, in the same State, Mr. D. Eckley Hunter counted 70 in 80 minutes. The numbers seen at New Haven were considerably greater. The fact that the display commenced before daylight had entirely closed seemed to indicate that only the termination of the shower had been observed in this country. Accordingly the display was soon found to have been witnessed from 60° E. to 90° W. of Greenwich, or through 150° of longitude. In England the first bolide of the swarm was seen by M. M. Brinkley, at 3 o'clock, P.M., in full daylight. The meteors were most numerous in the southern part of the continent, particularly in Italy. At the Observatory of Breslau, according to M. Faye, 3000 were seen from 6h. 30m. to 7h. 50m. Dr. Heis reported that at Münster 2500 per hour were counted by two observers. At Naples, Signor Gasparis observed two meteors per second. At Turin, M. Denza, Director of the Observatory, reported 33,400 in 6h. 30m.; many of various and delicate colors, and followed by long and brilliant trains. At some points the numbers were so great that an accurate enumeration was wholly impossible. In short, the display was decidedly the most brilliant that has occurred since that of November 13, 1833.
But some of the most interesting circumstances in connection with the phenomena of November 27, 1872, remain to be detailed. Astronomers without exception regarded the display as due to the earth's passage through the débris following in the path of Biela's comet. In accordance with this view Dr. Klinkerfues, of Gottingen, concluded that the comet itself, or rather its largest portion, ought to be found in the region of the heavens nearly opposite to that from which the meteoroids appeared to radiate.[27] As this point in the southern hemisphere could not be observed in Europe, he conceived the happy idea of detecting the fugitive by means of the electric telegraph. The following was accordingly dispatched to Mr. Pogson, Director of the Government Observatory at Madras, in Southern India: "Biela touched earth on 27th; search near Theta Centauri." The first two mornings after the receipt of this dispatch were cloudy at Madras. On the third, however, the cometary fragment was found, and its motion accurately measured. The observer described it as circular and rather bright, with no traces of a tail. But one fragment could be detected. On the next morning, December 3, the comet was again observed. Its diameter had sensibly increased; it had a bright nucleus, and still presented a circular aspect. A faint tail was also noticed, equal in length to one-fourth of the moon's apparent diameter. The following mornings being again cloudy, no further observations could be obtained. This cometary mass will be in close proximity to the earth about the last of November, 1892. Another brilliant meteoric shower may therefore be expected at that epoch.
The Meteors of April 20.
Meteoric showers have occurred about the 20th of April in the following years:
| B.C. | 687 | |
| 15 | ||
| A.D. | 582 | |
| 1093 | ||
| 1094 | ||
| 1095 | ||
| 1096 | ||
| 1122 | ||
| 1123 | ||
| 1803 |
The probability that these meteors are derived from a ring which intersects the earth's orbit, was first suggested by Arago in 1836. A comparison of dates led Herrick to designate 27 years as the probable period of the cluster. In the Astronomische Nachrichten, No. 1632, Dr. Weiss called attention to the fact that the orbit of the first comet of 1861 very nearly intersects that of the earth, in longitude 210°—the point passed by the latter at the epoch of the April meteoric shower. A relation between the meteors and the comet, indicating an approximate equality of periods, was thus suggested as probable. But the comet, according to Oppolzer, does not complete a revolution in less than 415 years. If, therefore, the meteoric period is nearly the same, the known dates of star-showers indicate a diffusion of meteoroids around one half of the orbit previous to the display of the year 15 B.C. No subsequent perturbation, then, of a particular part could sensibly effect the general orbit of the stream. The infrequency of the display renders, therefore, the hypothesis of a long period extremely improbable.
The entire interval between 687 B.C. and A.D. 1803 is 2490 years, or 92 periods of 27.0652 years; and the known dates are all satisfied by the following scheme:
| B.C. 687 to | B.C. 15 | ... 672 | years | = | 25 | periods of | 26.8800 y. | each. |
| 15 to | A.D. 582 | ... 597 | " | = | 22 | " | 27.1363 | " |
| A.D. 582 to | 1095 | ... 513 | " | = | 19 | " | 27.0000 | " |
| 1095 to | 1122 | ... 27 | " | = | 1 | " | 27.0000 | " |
| 1122 to | 1803 | ... 681 | " | = | 25 | " | 27.2400 | " |