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THE POPULAR SCIENCE MONTHLY.

to us the whole of living Nature, each varied offshoot fitly joined together, sloping gently back along the vast converging lines of ordinary generation to one grand starting-point, wherein till the fullness of time every living thing, from the microscopic diatom to the giant sequoia, and from the shapeless amœba to the stateliest of bipeds—

"Lay hidden, as the music of the moon

Sleeps in the plain eggs of the nightingale."
⁠Belgravia.

 

THE PLANET VULCAN.

By Professor DANIEL KIRKWOOD.

THE discovery of an intra-Mercurial planet during the total eclipse of July 29, 1878, has given new importance to any previous speculations on the question of its existence. A brief historical review of the subject will not be without interest.

In an article by the writer, "On the Probable Existence of Undiscovered Planets," written immediately after the discovery of Neptune, and published in the Literary Record and Journal of the Linnæan Association of Pennsylvania College,^[1] the question was thus considered:

"The distance from the centre of Jupiter to the nearest satellite is about three times the equatorial diameter of the primary. If, therefore, we suppose the distance of the nearest primary planet to have the same ratio to the diameter of the sun, the orbit of such planet will be somewhat less than 3,000,000 miles from the sun's centre. Consequently, in the interval of 37,000,000 miles there may be four planets, the orbit of the nearest having the dimensions above stated, and their respective distances increasing in the ratio of Mercury's distance to that of Venus. Such bodies, however, in consequence of their nearness to the sun, could hardly be detected except in transiting the solar disk."

It is well known that the disturbing influence of the other planets causes an advance in the position of Mercury's perihelion. In a century this change amounts to 10′ 43,″ which, according to Leverrier, is 38" more than can be accounted for by the influence of the known planets. This great astronomer inferred, therefore, that a planet, or possibly a zone of extremely small asteroids, must exist within the orbit of Mercury.

The conclusions of Leverrier were communicated to the French Academy in the autumn of 1859. Soon after their publication Dr. Lescarbault, an amateur astronomer as well as a medical practitioner of Orgères, some forty miles southwest of Paris, announced that, on March 26, 1859, he had observed the passage of a dark circular spot across

1. Vol. iii., April, 1847, p. 131.