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164 revolution. Besides, comets move across the orbits of the planets, and are jostled about as a man moving through a crowd. One planet pulls this way and another that, so that the comet's real course may differ much from the undisturbed orbit. In predicting the return of the great comet of 1556, another formidable source of error lies in the circumstance, that the observation of its appearance in 1264 was very imperfectly recorded. The most reliable accounts are those of the Chinese, who were at that period far in advance of European astronomers; still, tbey are not given with sufficient accuracy to enable us to predict the return within a single year. Assuming that the above dates are correct, the period is 292 years, and the comet, if it moved in an undisturbed orbit, should return in 1848. But allowing for the disturbance of planets, the probable period is about ten years longer. As we are now approaching the latest limit assigned by competent astronomers, it is natural that the first inquiry should be, on the discovery of a new comet, Is it the expected great comet? The comet of 1556 is named after Charles V., from the circumstance that its dreaded aspect is said to have led that monarch to cede the imperial crown to his son Ferdinand.

We are saved the necessity of any further speculation as to whether the comet Marguerit is the comet of Charles V., by learning, while we write, that Leverrier has authoritatively decided the matter. He has