PHILOSOPHICAL SOCIETY OF WASHINGTON. 161 



and three-fifths more, while the former has expended two-fifths of 

 its original velocity. 



Here then is presented a new difficulty on the kinematic theory. 

 In what possible manner can a body moving at a definite rate im- 

 part to another body by simple impact a velocity considerably higher 

 than that possessed by itself? By kinematics, this question also 

 must remain forever unanswered. By the established principles of 

 dynamics — there being no actual or mathematical contact of the 

 two balls, — the static energy of their combined compressions or 

 repulsions acquired during the time of their physical contact pre- 

 cisely equals the kinetic energy of impact ; and consequently on 

 resilience refunds a precisely equal kinetic energy of separation ; — 

 to wit, a relative velocity of 10 feet per second. 



Impossibility of Action at no Distance. — It turns out therefore 

 when we examine very slightly beneath the surface of " sense in- 

 formation," that impulsion (so perfectly obvious and intelligible to 

 the kinematist) is itself a very notable example of the ultra-sensible 

 and recondite : * — that the vaunted philosophy of " the sense of 

 touch " is no more able to escape from the dominion of the unseen, 

 the hidden, the enigmatical, in causation, than is the dynamism 

 which is held to be so superficial, credulous, and undiscerning. 



And this mysterious but necessary principle of all dynamics 

 reaches far back of the imagined cases of corporeal contact in col- 

 lisions, — even to the intimate structure of the densest material ; f 



*As acutely remarked by the eminent mathematician — James Ivory : 

 "A little reflection is sufficient to show that in reality we have no clearer 

 notion of impulse as the cause of motion, than we have of attraction. We 

 can as little give a satisfactory reason why motion should pass out of one 

 body into another on their contact, as we can why one body should begin 

 to move, or have its motion increased, when it is placed near another body. 

 - - - If then we are apt to think that impulse is a clearer physical 

 principle than attraction, there is really no good ground for the distinction ; 

 it bas its origin in prejudice." {Encyclopaedia Britannica. 8th ed. 1854 : 

 art. "Attraction: " vol iv, p. 220.) 



" When the Newtonians were accused of introducing into philosophy an 

 unknown cause which they termed attraction, they justly replied that they 

 knew as much respecting attraction as their opponents did about impulse." 

 Dr. William Whewell. {History of Scientific Ideas. 1858 : book in, 

 chap, ix, sect. 8 : vol. i, p. 278.) 



f There is good reason to think that absolute contact never takes place in 

 the component parts of the hardest and most compact solid bodies. ' ' James 

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