6 Mr. J. Croll on What determines Molecular Motion F — ■ 



cause of the path being taken, we should then understand the law of 

 the moving particles ; we should then perceive how the selection 

 of the particular path was a necessary result of something within 

 our knowledge. A prodigious number of physical phenomena 

 are perceived to follow as necessary consequences from Newton's 

 grand law, that bodies tend toward each other with a force vary- 

 ing inversely as the square of the distance and directly as the 

 mass of the bodies. But we should reach a higher unity and 

 obtain a deeper insight into nature did we know not merely the 

 empirical fact that bodies do so, but the cause why they do so. 

 It is this which incites in the rational physicist the desire to find 

 out the cause of gravity. 



But be all this as it may, whether it be Cause or Law, that is the 

 thing which we are really in search of, every one will admit that 

 the problem of deepest interest is, what causes the molecules 

 and particles of living nature to arrange themselves into organic 

 forms ? The problem is not what moves the particles, but what 

 determines or directs the motion — or, in other words, what is the 

 cause of the determination of motion ? 



What, then, determines molecular motion in organic nature ? 

 What determines and directs the action of the forces concerned 

 in the production of specific forms in the inorganic and organic 

 world ? Is it a Force ? This leads us to the second proposition, 

 viz. 



(2) The action of a Force cannot he Determined hy a Force, 

 nor can Motion he Determined hy Motion. 



That the action of a force cannot be determined by the action 

 of a force is demonstrable thus. If the action of a force is de- 

 termined by an act, then this determining act must itself have 

 been determined by a preceding act ; and this preceding act by 

 another, and so on in like manner to infinity. This is evident; 

 for if the act which determines the action of the force exist at 

 all, it must exist in time and space, and must have a determinate 

 existence in reference to time and space, and if so, something 

 must have given it that determinate relation. If it be replied 

 that it was a prior act which determined this determining act, 

 then that prior act in order to give the determining act the 

 proper determination must itself have been already properly de- 

 termined; and the question again recurs, what gave this prior 

 act the proper determination ? If the determination was given 

 by an act still prior, that act must itself have been properly de- 

 termined ; and if so, then there must have been another act pre- 

 ceding which gave it the proper determination, and so in the like 

 manner to infinity. The reason of all this is perfectly obvious. 

 When we account for the determination of an act by assigning 



