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HISTORICAL VIEW OF THE

will not fall exactly in a pe. pendicular line, but will de-viate towards the east. Hooke entered upon the subjectboth experimentally and theoretically : he verified thefact, and improved upon the theory, by showing thatthe deviation ought to be a little to the south-east, thedirection of gravity being (except at the equator) obliqueto the earth’s axis of rotation. This topic being dis-cussed, led to the further question, in what line thebody would descend. Newton, it appears, had inferredthat it would be a species of spiral, owing to the resist-ance of the air. Hooke alleged that in vacuo it oughtto be a portion of an ellipse, but he assigned no reasonor proof of this. Nor could he do so afterwards, whenearnestly pressed, both by Halley and Wren, to give ademonstration. It was about this time that his otherspeculations, to which we have before referred, ongravity, &c., were communicated to the Royal Society .It is probable that, at this time, Newton had succeededin investigating some of those dynamical problems re-specting elliptic nation, to which we have before ad-verted. Still, these were mere abstract speculations, thelofty exercises of a mathematical genius of the highestorder, but which, as it yet seemed, were not to be re-cognised in nature; so far, that is, as the accuracy ofobservation had then extended.

But upon what did the insufficiency of Newton's cal-culated result depend ? Might not the numerical valuesassumed be open to question ? The orbit and distance ofthe moon were so well ascertained, by the long-continuedlabours of astronomers, that with respect to them therecould be little doubt. Not so the magnitude of the earth.We have already seen how slow was the advance toaccuracy, in obtaining this result from the measurementof arcs of the meridian. The more accurate determin-ation of Picard had, however, now been effected ; andhis recent result became the subject of discussion at ameeting of the Royal Society , in June, 1682. Newton,being present, felt, of course, a degree of interest inthe discussion, totally unsuspected by the bystanders.