IMITATION AMONG ATOMS AND ORGANISMS. 509 



of lime, and the uniform tenacity of solutions of soap in water, 

 as shown in experiments with soap bubbles, both illustrate how 

 equably substances held in solution are diffused. The evapora- 

 tion of fluids into air, like the dissolution of solids in water, is in 

 its results, at any rate, a case of assimilation to the character of 

 the surrounding or adjacent medium ; so that, the more we heat 

 a bar of iron, the more progress does it make toward that vapor- 

 ous condition in which it can easily be diffused through its en- 

 vironment. The mixing of metals also illustrates diffusion ; for, 

 whether it results in amalgams or alloys, whether the mixture 

 be a merely mechanical association of the parts brought together 

 or a chemical combination of those parts, the fact remains that 

 for given areas, which may be large or small, the average degree 

 of diffusion is the same. This is shown with especial clearness 

 in those compounds of carbon and manganese with iron needed 

 for a variety of industrial pur]30ses, since such compounds 

 would have none of their present commercial value were it not 

 for the uniform diffusion through the iron of the substance em- 

 ployed to modify it. 



Here, then, our treatment of the subject must draw to a close. 

 While necessarily brief, it has been complete enough to reveal 

 a process far reaching in its scope and of cosmical significance. 

 We have seen how like units everywhere tend to be associated 

 and unlikes dissociated ; how unlikes, held in forcible association, 

 tend to be more or less profoundly assimilated to one another ; 

 and how disturbances of prevailing uniformity tend to be equa- 

 bly distributed through the several media in which they occur. 

 But we have also noted that the power impelling to these multi- 

 farious acts of assimilation, to these movements of association 

 and dissociation, is not the power of the units themselves, but 

 the power of the system to which they immediately belong ; and 

 we are thus warned of the important bearing which our law has 

 upon two problems of the utmost generality in physics namely, 

 the problems of chemical affinity and gravitation. It is true that 

 we have as yet no formula for explaining these manifestations of 

 power by a single principle ; that we do not yet know the real 

 structure of ether ; and that there is still needed a definite account 

 of gravitation as an intelligible mechanical process. Nevertheless, 

 the causal connection of both gravitative and chemical actions 

 with the ether system is already obvious to physicists. That the 

 power which accomplishes these actions does not reside in matter 

 alone, but resides also in the ether system is, in fact, a function 

 of that system regarded as including both ether and matter 

 seems to be increasingly pointed to by the trend of recent phys- 

 ical research. Basing our final conjecture, therefore, on general- 

 ization from a wide array of facts, it may not be premature to 



