OF THE DISCOVERIES OF

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ninety-five millions of miles, to a fourth number,which is the cube of Vcnus’s mean distance fromthe fun ; and if the cube root of this number befound, it will give about sixty-eight millions ofmiles for her real mean distance; so that, by thisrule, if the times of the periodical revolutions ofthe planets be known, and the mean distance ofany one of them. from the fun, the mean distancesof all the rest may he determined by a simpleproportion. And this rule is not only applicableto the planets, but it is also equally true withrespect to their satellites or attendants; themoons of Jupiter and Saturn are found to followshe fame law in revolving round their primaries,which is observed by those primaries in revolvinground the sun,

These are the discoveries hy which Kepler en-riched the science, and obtained an immortalityof renown: but it must be observed, that he whohad subjected the planetary motions to invariablylaws, was unable, with all his penetration, to findout tjie reason of them. Nature had shownhim some of her most secret operations, buta more complete knowledge of them was re*served for Newton. Among a number of in-genious guesses which he has made upon thissubject, there are some as novel as they aresingular. He considers the stars and planets asshe inhabitants of ether, which live and move inthat element like butterflies in the air; or as

plants