266

HISTORICAL VIEW OF THE

ing powers are so much the more powerful in operating,by how much the nearer the body wrought upon is totheir own centres. Now. what these several degrees are,I have not yet experimentally verified: but it is anotion which, if fully prosecuted, as it ought to be, willmightily assist the astronomers to reduce all the celes-tial motions to a certain rule, which I doubt will neverbe done without it. He that understands the nature ofthe circular pendulum and circular motion will easilyunderstand the whole of this principle, and will knowwhere to find directions in nature for the true statingthereof. This I only hint at present to such as haveability and opportunity of prosecuting this enquiry,and are not wanting of industry for observing and cal-culating, wishing heartily such may be found, havingmyself many other things in hand, which I would firstcomplete, and therefore cannot so well attend to it.But this I do not promise the undertaker, that he willfind all the great motions of the world to be influencedby this principle, and that the true understandingthereof will be the true perfection of astronomy.”

This passage (though much misunderstood by De-lambre,) is extremely interesting, both as showing hownearly Hooke approached to a correct conception ofthe truth so soon afterwards developed by Newton,and also as giving his own confession as to the pointsin which he had failed in gaining possession of thewhole truth.

Dr. Wallis, in 1666, also threw out some ideas ofthe same kind, and remarked, “ to the objection thatit appears not how two bodies that have no tie canhave one common centre of gravity, I shall onlyanswer, that it is harder to show how they have it thanthat they have it.”

In 16'83, sir C.Wren stated that, several years before,he had endeavoured to explain the planetary motions“ by the composition of a descent towards the sun, andan impressed motion, but he at length gave it over, notfinding the means of doing it.”