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This possibility seemed to be realized by Chandler's identification of Brooks's and Lexell's comet. An exceedingly close approach to Jupiter in 1886 had, he found reason to believe, produced such extensive alterations in the elements of its motion as to bring the errant body back to our neighbourhood in 1889. But his inference, though ratified by Mr.
A telescopic comet with a period of 7-1/2 years, discovered November 22, 1843, by M. Faye of the Paris Observatory, formed the subject of a characteristically patient and profound inquiry on the part of Leverrier, designed to test its suggested identity with Lexell's comet of 1770.
A famous example of this kind of planetary horse-play is furnished by the story of Lexell's missing comet. This comet was first seen in 1770. Investigation showed that it was moving in an orbit which should bring it back to perihelion every five and a half years; yet it had never been seen before and, although often searched for, has never been seen since.
The belief in the comet's surpassing thinness and lightness is not a mere speculative opinion. It rests upon incontrovertible proof. In 1770, Lexell's Comet passed within six times the moon's distance of the earth, and was considerably retarded in its motion by the terrestrial attraction.
Crossing as they often do the paths of the planets in their progress to and from their perihelia, it cannot but be that they should now and then come in contact with one of these spheres. One, called Lexell's, did come athwart the satellites of Jupiter in 1769, and once again in 1779, so as to be deranged in its own course.
Laplace had shown that if the amount of matter forming Lexell's comet had been as much as 1/5000 of that contained in our globe, the effect of its attraction, on the occasion of its approach within 1,438,000 miles of the earth, July 1, 1770, must have been apparent in the lengthening of the year.
A cause for the disruption it had presumably undergone had, before then, been plausibly assigned. The adventures of Lexell's comet have long served to exemplify the effects of Jupiter's despotic sway over such bodies.
They sometimes, however, yield too much to temptation, and have to suffer the penalty of a short imprisonment in consequence. Lexell's Comet, for instance, rushed in its hyperbolic path too near to Jupiter, and was caught in the attraction of its mass, and made to dance attendance on the sun through two successive elliptical revolutions.
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