352 NATURE AND MAN 



of that mutual repulsion, to give motion to the various solid 

 parts of which the machine is composed. And thus, if asked 

 what is the cause of the movement of the steam-engine, we dis- 

 tinguish in our reply between the dynamical condition supplied 

 by the heat, and the material condition (or assemblage of con- 

 ditions) afforded by the " collocation " of the boiler, cylinder, 

 piston, valves, etc. ... In like manner, if we inquire into the 

 cause of the germination of a seed — which has been brought to 

 the surface of the earth, after remaining dormant through having 

 been buried deep beneath the soil for (it may be) thousands 

 of years — we are told that the phenomenon depends upon 

 warmth, moisture, and oxygen ; but out of these we single 

 warmth as the dynamical condition, whilst the oxygen and the 

 water, with the organized structure of the seed itself, and the 

 organic compounds which are stored up in its substance, con- 

 stitute the material. 

 The subsequent general recognition by the scientific world of 

 the "correlation" between the forces of nature (under whatever 

 form expressed) has thus given a breadth of foundation to the 

 dynamical doctrine of causation which it previously lacked ; and 

 the doctrine having been afterwards formally developed by Pro- 

 fessor Bain, was summarized by J. S. Mill in the later editions of 

 his " Logic," almost in the very terms in which I had originally 

 propounded it to him in conversation, and had publicly expressed 

 it in the extract just cited : — " The chief practical conclusion 

 " drawn by Professor Bain, bearing on causation, is that we must 

 " distinguish in the assemblage of conditions which constitutes 

 " the cause of a phenomenon, two elements : one, the presence 

 " of a force ; the other, the collocation or position of objects 

 " which is required in order that the force may undergo the par- 

 " ticular transmutation which constitutes the phenomenon." * 

 Mr. Mill himself still preferred, however, to express the principle 

 in terms of motion, rather than in terms of force: — "If the 

 " effect, or any part of the effect, to be accounted for consists in 

 " putting matter in motion, then any of the objects present which 

 " has lost motion has contributed to the effect ; and this is the 

 " true meaning of the proposition that the cause is that one of 



* "System of Logic" (eighth edition), vol. i. p. 406. 



