Page:Popular Science Monthly Volume 89.djvu/521

 Popular Science Monthly

��the larger or more brilliant of the two was seen to have three tails arranged at equal angular inter\als about it. One of these tails extcndeti over to the smaller comet and tormed some kind of connec- tion with it. There was in fact a bridge of light between the two. The two comets were again seen in 185', when they were still traveling along together. The interval between them, which was less than 200,000 miles in 1846, had now increased to 1,270,000. The comet seems never to have been certainly seen since this occasion. But, what was certainly seen was a great shower of "shooting stars." These luminous meteors seemed to radiate from just about the point whej-e the orbits of Biela's Comet and of our earth cross each other. The date of the star-shower was some twelve weeks later than the time when the comet itself should have made the crossing. What these facts, when considered in the light of still other information of an astronom- ical character, mean is probably this: After 1852, Biela's Comet broke up into small bits of matter. These possessed individually the onward motion of the comet and were held in restraint by the sun (and any nearby planets), so that the pieces generally followed the orbit which the comet itself had been pursuing. The result was a long stream of very small heavenly bodies. When on No- vember 27, 1872, a part of this stream came within the reach of the attractive power of the earth, the separate bodies fell through our atmosphere. The friction of the enormously rapid move- ment resulted in heating them up to incandescence. These fragments of the original comet thus became luminous meteors or "shooting stars." In 1798 and 1838, there were notable showers of stars at times and places which were near the position and time calculated for Biela's Comet for those years. These showers, in contrailistinction to that of 1872, seem to ha\e preceded the comet, itself. In fact, putting everything to- gether, there would appear to have been a stream of small bodies five hundred million miles in length.

The foregoing suggests that when a comet is lost, the real fact may be that it has burst into multitudes of fragments.

Another comet which belongs to the

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list of the lost ones was first disco\ered in August, 1844. Apparently, Di Vico was the first to get even a telescopic glimpse of it. However, the comet rapidly approached our neighborhood, so that it was not long until it was visible to the naked eye. Di Vico's Comet was found to be traveling in a closed, or elliptic, orbit of such a charac- ter that it would return once in e\'ery period of a little less than five and one half years. The next return woukl accordingly be in the early part of 1850. Unfortunately, the comet, if it really returned, was too unfavorably situated with respect to the sun to be seen. Howe\er, in 1855, conditions would be advantageous. But no comet was seen then. Nor has this body ever certainly been seen since.

What Became of the Comet of 1264 ?

One of the most notable of the heaven- ly bodies which ha\-e more or less title to a place amongst the lost comets is the comet of 1264. This body engaged the attention both of Chinese and European writers. In 1556, another great cometar>- \ision was seen in the sky in Europe and in China. Astrono- mers who studied the a\ailable data con- cluded that the two were one and the same comet. Calculations indicated that the period of revolution about the sun was somewhere in the neighborhood of three hundred and two to three hundred and eight years. Consequently, this great comet should have reappeared in 1858 or within a few years afterwards. It has, apparently, disappeared fore\'er. In the year 975, a great comet was seen whose course has been thought by one astronomer to ha^■e possibK' been that of the comet of 1264 at that time.

It is of interest to note that a comet may disappear because its elliptic orbit has been deranged into a parabola or an hyperbola. Sir Lsaac Newton showed that a body controlled by onx sun moves in a curve which is some one of the sections of a cone — that is, either an ellipse, a parabola or an hyperbola. As the latter two are open curves, a comet which pursued such a path would go olY into space never to reappear. A de- rangement of orbit from closed to open curve has doubtless happened often.

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