FOOTNOTES:
[1] N. A. Review, Vol. LVI., pp. 339–351.
[2] "It is inconceivable, that inanimate brute matter should, without the mediation of something else, which is not material, operate upon and affect other matter without mutual contact, as it must, if gravitation, in the sense of Epicurus, be essential and inherent in it. And this is one reason why I desired you would not ascribe innate gravity to me. That gravity should be innate, inherent, and essential to matter, so that one body may act upon another at a distance through a vacuum, without the mediation of any thing else, by and through which their action and force may be conveyed from one to another, is to me so great an absurdity, that I believe no man, who has in philosophical matters a competent faculty of thinking, can ever fall into it. Gravity must be caused by an agent acting constantly according to certain laws."—Newton's letter in Bentley's Works, Vol. III., pp. 211, 212.
[3] And yet, so strong is the propensity to metaphor, that scientific men talk of the vis inertiæ as a true force, though the ideas expressed by the two Latin words are certainly incongruous. The mistake here arises from confounding inertness, or resistance to force,—a merely negative idea,—with the true force which is necessary to overcome it; or rather, since force can only be measured by its results, and must always be adequate to the effect produced, inquirers have adopted the convenient hypothesis of two antagonistic forces, not always recollecting that one of them is merely passive.