49± SEGREGATION. 



any two units or portions of matter which are unlike in size, 

 weight, form, or other attribute, can be known by us as un- 

 like only through some unlikeness in the forces they impress 

 on our consciousness; and hence this unlikeness also, is 

 constituted by the presence in the one of some force or forces 

 not present in the other. Such being the common nature of 

 these unlikenesses, what is the inevitable corollary? Any 

 unlikeness in the incident forces, where the things acted on 

 are alike, must generate a difference between the effects; 

 since otherwise, the differential force produces no effect, and 

 force is not persistent. Any unlikeness in the things acted 

 on, where the incident forces are alike, must generate a dif- 

 ference between the effects; since otherwise, the differential 

 force whereby these things are made unlike, produces no ef- 

 fect, and force is not persistent. While, conversely, if the 

 forces acting and the things acted on, are alike, the effects 

 must be alike; since otherwise, a differential effect can be 

 produced without a differential cause, and force is not per- 

 sistent. 



Thus these general truths being necessary implications 

 of the persistence of force, all the re-distributions above 

 traced out as characterizing Evolution in its various phases, 

 are also implications of the persistence of force. Such por- 

 tions of the permanently effective forces acting on any ag- 

 gregate, as produce sensible motions in its parts, cannot but 

 work the segregations which we see take place. If of the 

 mixed units making up such aggregate, those of the same 

 kind have like motions impressed on them by a uniform 

 force, while units of another kind are moved by this uniform 

 force in ways more or less unlike the ways in which those 

 of the first kind are moved, the two kinds must separate and 

 integrate. If the units are alike and the forces unlike, a 

 division of the differently affected units is equally necessi- 

 tated. Thus there inevitably arises the demarcated group- 

 ing which we everywhere see. By virtue of this segregation 

 that grows ever more decided while there remains any possi- 



