4 Mr. J. Croll on What determines Molecular Motion?— - 



motion, but what produces the particular kind of motion ? It 

 is not what gives existence to the motion, but what determines 

 its direction ? This is evident, because the particular phenome- 

 non, regarding which our inquiries are concerned, does not di- 

 rectly depend upon the mere existence of the motion, but upon 

 its special direction or determination. The same exertion of 

 force which produces one phenomenon would probably produce 

 any other phenomenon, were determination in the proper direc- 

 tion given to it. It is the determination of the force which 

 accounts for the particular phenomenon ; the mere exertion of 

 force may be supposed to be the same in all phenomena. We 

 are therefore led to the following proposition, viz. : — 



(I) The Production of Motion and the Determination of Motion 

 are absolutely and essentially different. 



The radical and essential distinction between motion and the 

 determination of motion could not possibly have escaped the 

 observation of physicists ; but the important bearing that this 

 distinction has on physical inquiry has certainly been overlooked. 



In physics we have been accustomed to attribute every thing 

 to force ; force, at least, has always been regarded as the all-im- 

 portant element. This, however, is a mistake ; for, as we shall 

 see, far more depends upon the determination of force than upon 

 its existence, and therefore, unless force le determined by force, the 

 most important element in physical causation is a something differ- 

 ent from force. And this holds equally true whether our inqui- 

 ries relate to the inorganic or to the organic world. 



In the production of organic forms from the simplest up to 

 the most special and complex in the vegetable and animal king- 

 dom two things require to be accounted for, viz. (1) the motion 

 of the matter of which they are composed, and (2) its disposition 

 or arrangement with reference to time and space. The particles 

 which are to compose the organism must not only move, but 

 move with a particular determination in regard to time and 

 space. If a molecule has to be placed in any particular place 

 of an organism, it must move in the particular direction in space 

 which will lead to that place, and stop at the particular moment 

 of time when it reaches it. 



Motion is not only produced, but it is produced in a particular 

 manner and under particular conditions or determinations in re- 

 gard to time and space and other circumstances. In other 

 words, not only must something produce the motion, but some- 

 thing must determine it also. The causing of, or giving mere 

 existence to the motion, I have called the Production of the 

 motion. The causing of it to happen in the particular manner 

 in which it does, rather than in some other manner, I have called 



