Page:Popular Science Monthly Volume 16.djvu/262

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248

THE POPULAR SCIENCE MONTHLY.

tronomical Society, that no object has thrown more light on the general nature of cometic bodies than the comet known as Biela's. I propose now to give a brief sketch of the history of this interesting body, and then to consider the reasons why astronomers expect that during the last week of November, 1879, there will be a display of shooting stars as the earth passes through the comet's track.

In the year 1826 Biela discovered a comet, the path of which was calculated by Gambart, a French astronomer, insomuch that, according to the usual rule in such cases, the comet should be called Gambart's, not Biela's. It was found to revolve around the sun in a period of about six and two thirds years. It was not a conspicuous body—in fact, it has seldom been much more than barely visible under the most favorable conditions by the naked eye. Yet it differed from most telescopic comets in showing not only a nucleus and a coma, but a tail also. In 1832, 1839, and 1846, this comet returned to the earth's neighborhood, and on two of these occasions it was well seen. In 1839 it was so situated as to be lost in the sun's rays. In fact, at every third return astronomers knew that it would be hopeless to search for the comet. Thus, it was discovered in 1826, and well seen in 1832, but not seen and not even looked for in 1839. So, again, it was seen in 1846 in its calculated place, and again in 1852, but it was not looked for in 1859. In 1866 and 1872 it should have been visible, but, as will presently be explained more fully, it was not seen. In this present year, 1879, supposing all had gone on as in the forty preceding years, the comet would not have been visible, passing too near the sun's place in the sky. Astronomers have been set to search for it this year (but quite fruitlessly), because there were reasons to believe that, if seen at all, the comet would not be seen on its former track. But we must not pass to this part of the comet's history until the strange circumstances connected with former returns and with former expected returns of the comet to visibility have been briefly considered.

In the year 1846, when Biela's comet was well seen, it divided—or rather, after having apparently been single, it was seen to be divided—into two distinct comets, each having coma, nucleus, and a short tail of its own. These two comets traveled along side by side until they passed out of view; but in 1852 both returned into view, though the distance between them was then greatly increased. Whether in 1859 the companion comets would have been seen had the earth been more favorably situated, is not known. The comet was not even looked for in that year, so hopeless did the search seem for so faint an object, close as the comet then was to the sun's apparent place in the sky. But in 1866 the comet should have been seen as favorably as in 1846. The superintendent of the "Nautical Almanac" published an ephermis of the comet's motions—in other words, he stated where the comet was to be looked for day after day, and a number of the most skillful practical observers in Europe searched carefully for it, but it