THE LAWS OF MOTION 299 



felt justified in hoping for, it is largely because we have 

 had no second Laplace to deal with " the infinitely little," 

 as the first Laplace dealt with " the infinitely large." 

 The mechanical theory Laplace foreshadowed will never 

 enable us to assert that such an event must of necessity 

 have occurred in the past or must unquestionably occur in 

 the future. But the description in terms of motion, the 

 brief formula expressing the changes in time and space of 

 geometrical concepts, is the whole content of natural 

 science,^ and we ought rather to wonder at the enormous 

 power this conceptual model even at present gives us of 

 understanding the recorded past and of anticipating the 

 experiences of the future, than idly criticise the "incapacity " 

 of one who has done more than any other scientific worker 

 of the nineteenth century to advance our conceptual notions 

 in the mechanical field. 



^ 7. — The Fourth Law of Motion 



It is high time, however, that we should return to our 

 discussion on the laws of motion, and, assuming for the 

 present that relative position is the principal factor in the 

 determination of mutual accelerations, we must ask what 

 more exact laws may be postulated with regard to these 

 accelerations. We have in the first place to investigate 

 how far the individuality of the dancers is to be conceived 

 as influencing the manner in which they spurt each other's 

 motion. Do any two dancers, whatever their race and 

 family, and under whatever surroundings they may meet, 

 always dance in the same fashion whenever they come to 

 the same position ? Or must we consider it necessary to 

 classify our corpuscles by some scale which may itself 

 indeed change with a change in the field ? Again, are 

 two dancers to be conceived as dancing in the same 

 manner whatever aspect (p. 197) they bear to each other, 



' I use this word purposely, for I allow no distinction ultimately between 

 the physical and biological branches of science. As the latter advance, mere 

 descriptions of sequences of sense-impressions are more and more likely to be 

 replaced by formula describing conceptual motions ; such is, indeed, the 

 confessed aim of those somewhat embryonic studies "cellular dynamics" 

 and " protoplasmic mechanics." 



