PHILOSOPHICAL SOCIETY OF WASHINGTON. 159 



space, a fortiori must static "force" require distance as the indis- 

 pensable condition of its action. 



So much therefore for the vaunted dictum of "common-sense:" 

 and so much for the antagonistic dictum whose " absurdity is so 

 great that no man who has in philosophical matters a competent 

 faculty of thinking can ever fall into it!"* And this absurd — this 

 incomprehensible — this inconceivable proposition — that matter is 

 capable of acting only where it is not, is proved by the incontestible 

 conviction of reason to be a primary and necessary truth: and the 

 wondrous scholastic dogma resisting it — supposed the sacred oracle 

 of a mysterious intuition, — is but the detected impostor of a crude 

 induction. 



True meaning of Contact Action. — To confirm however the explicit 

 deductions of mechanical theory by the verifications of actual ex- 

 perience, let us examine more closely the true character of that 

 transmission of energy by impact which to the kinematist appears 

 to furnish so simple and so obvious an explanation of " force." 

 Taking the most elementary example of the vis a tergo, let us sup- 

 pose two precisely similar billiard-balls — A and B — on the perfectly 

 smooth surface of a frozen lake, B at rest, and A rolled toward it 

 in the direct line joining their centers of inertia. The familiar re- 

 sult that A is brought to rest by the collision, and B continues the 

 motion in the same direction prolonged, will be fluently explained 

 by the kinematist as a mere case of conservation, or the persistence 

 of motion, — which evidently passes at the instant of contact directly 

 from A to B, like an electric charge. 



Overlooking — first, the fallacy of a finite velocity passing into a 

 body instantaneously (already controverted), there is a second diffi- 

 culty, that motion — defined as a change of position in a body, or 

 the occupation of successive portions of space by a body, — cannot 

 exist out of the body, cannot therefore pass through the confines of 

 the body. But admitting for the moment both these possibilities, — 

 in the third place, how could the ball A part with all its motion to 



*This inconsiderate utterance of Newton in his oft-quoted " third Bent- 

 ley letter," (Feb. 25, 1693,) was wholly repudiated by him a quarter of a 

 century later, when with a graver wisdom he asked the question : " Have 

 not the small particles of bodies certain powers, virtues, or forces, by which 

 they act at a distance?" {Optics. 2d edition. 1717: book III, query 31.) 

 A recantation never cited by the kinematist. 



