UNEQUAL ACTION OF CAUSES 165 



definite amount, equivalent in value, of the other is pro 

 duced in its stead. Joule proved, by numerous experi- 

 ments, that the mechanical force of 1 Ib. weight falling 

 through 772*55 feet in height was sufficient, when con- 

 verted into heat, to raise the temperature of 1 Ib. weight 

 of water 1 Fahr. Transformations of other farces have 

 been effected, and their equivalents determined. 



XII. The principle of transference of force flows from 

 the principle of equivalence of forces, and affirms that 

 whenever one substance loses a certain amount of force, 

 another substance acquires a precisely similar quantity. 



XIII. The principle of concurrence of causes includes 

 those cases in which a number of different causes conspire 

 to produce a single effect. It is by a concurrence of causes 

 that any special result of manufacture or art is produced ; 

 that a ship or a railway train arrives safely or otherwise at 

 its destination ; that an invalid either dies or is restored to 

 health, &c. Most of the concrete phenomena of ordinary 

 life may be referred to this principle. It is either by the 

 simple action, multiplication, division, combination, or 

 permutation of causes, that the varied and successive 

 phenomena of the universe are produced. 



XIV. The principle of unequal action of causes 

 (either producing or resisting ones) enables a single cause 

 to produce a multiplication of effects and a number of 

 phenomena, each of which becomes in its turn a cause,, 

 and produces many effects. It gives rise to ' differentia- 

 tion ' in all its forms ; to the irregular directions of 

 accretion of all inanimate substances, and of growth of 

 living things ; and thus to the development of the varied 

 forms of minerals, vegetables, and animals. In accordance 

 with this principle, every inanimate substance and every 

 living thing takes the path of least resistance ; every 

 stream and river takes the easiest course; men avoid 



