MATTER, MOTION, AND FORCE 



we call the conditions, we cannot affirm that the 

 effects will differ, without affirming either that 

 some force has come into existence or that some 

 force has ceased to exist. If the cooperative 

 forces in the one case are equal to those in the 

 other, each to each, in distribution and amount, 

 then it is impossible to conceive the product of 

 their joint action in the one case as unlike that 

 in the other, without conceiving one or more of 

 the forces to have increased or diminished in 

 quantity ; and this is conceiving that force is 

 not persistent." 1 It follows, therefore, from the 

 persistence of force, that there is an invariable 

 order of succession between the totality of phe- 

 nomena which exist at any given instant and the 

 totality of phenomena which exist at the next 

 succeeding instant. No matter how many spe- 

 cial orders of sequences may interlace to form 

 the grand web of sequent phenomena, the order 

 of sequences, both separately and in the ag- 

 gregate, must be invariable. In complicated 

 mechanical problems, where many forces are 

 involved, we proceed to eliminate one after an- 

 other by means of the principle of the parallel- 

 ogram of forces, until at last we retain but two 

 differently located forces, the resultant of which 

 is easily calculable. So, in the most complex 

 cases of causation to be found in nature — as, 

 for instance, in those concerned in the develop- 



1 First Principles, p. 193. 



*5* 



