essential to Matter, Sec. 71

XXV. From what has been said we mayobserve, how wisely animal bodies are tieddown to this great body of the earth, by theconstant impulse of gravitation * for sincethere could be no progressive motion withoutthe resistance and re-action of such a firmsustentacle, if by any cause or accident, a liv-ing creature were once detached from theearth, at whatever distance, it should be fixedthere, as in setters, without being able to re-turn, or move in any direction. And thismust happen, on many necessary occasions,both to man and beast. In running swiftly,in offering to leap, in making many neces-sary efforts, they would lose their hold ofthe earth, fly from it, and at length remainsuspended, for want of something to resisttheir efforts to bring themselves down again(if the distinction of down and up did notthen evanisti; which if it did, I omit to markthe influence it would have on the animalœconomy). Their whole body might per-haps turn some way on its own center of gra-vity, by the struggle of the limbs amongthemselves, between which a resistance andre-action would still be given ; but this wouldnever advance the center of gravity itself, norF 4 therefore