TRANSFORMATION AND EQUIVALENCE OF FORCES. 229 



acid. Solar forces millions of years ago expended on the 

 Earth's vegetation, and since locked up beneath its surface, 

 now smelt the metals required for our machines, turn the 

 lathes by which the machines are shaped, work them when 

 put together, and distribute the fabrics they produce. And 

 in so far as economy of labour makes possible the support 

 of a larger population ; gives a surplus of human power that 

 would else be absorbed in manual occupations ; and it facili- 

 tates the development of higher kinds of activity; it is clear 

 that these social forces which are directly correlated with 

 physical forces anciently derived from the sun, are only 

 less important than those whose correlates are the vital forces 

 recently derived from it. 



§ 73. Regarded as an induction, the doctrine set forth in 

 this chapter will most likely be met by a demurrer. Many 

 who admit that among physical phenomena at least, trans- 

 formation of forces is now established, will probably say that 

 inquiry has not yet gone far enough to enable us to predicate 

 equivalence. And in respect of the forces classed as vital, 

 mental, and social, the evidence assigned, however little to 

 be explained away, they will consider by no means conclu- 

 sive even of transformation, much less of equivalence. 



To those who think thus, it must now however be pointed 

 out, that the universal truth above illustrated under its vari- 

 ous aspects, is a necessary corollary from the persistence 

 of force. Setting out with the proposition that force can 

 neither come into existence, nor cease to exist, the several 

 foregoing general conclusions inevitably follow. Each 

 manifestation of force can be interpreted only as the effect 

 of some antecedent force : no matter whether it be an inor- 

 ganic action, an animal movement, a thought, or a feeling. 

 Either this must be conceded, or else it must be asserted that 

 our successive states of consciousness are self -created. Either 

 mental energies, as well as. bodily ones, are quantitatively 

 correlated to certain energies expended in their production, 



