160 HELMHOLTZ ON THE CONSERVATION OF FORCE. 



motion of the conductors towards each other, furnishes a cur- 

 rent which itself is unchanged by the induction, is equal to the 

 change of its potential towards the other conductor which 



is traversed by — • In this form the law is deduced by 



Neumann from the analogy of the magnetic and electro-dynamic 

 forces, 1. c. § 10, and he extends it also to the case where the 

 induction in motionless conductors is effected by the strength- 

 ening or weakening of the current. W. Weber shows the coin- 

 cidence of his assumption, with regard to the electro-dynamic 

 forces, with these theorems, 1. c. p. 147-153. From the law of 

 the conservation of forces we do not obtain any determination for 

 this case ; by the reaction of the induced upon the inducing 

 current a weakening of the latter must occur, which corresponds 

 to a loss of heat equivalent to that gained in the induced cur- 

 rent. In the action of the current upon itself, the same relation 

 must exist between the weakening of the current at the com- 

 mencement, and the extra current. No further consequences 

 can however be deduced here, inasmuch as the form of the 

 augmentation of the currents is not known, and besides this the 

 law of Ohm is not immediately applicable. 



Of known natural processes those of organic existences are 

 still to be considered. In plants the processes are chiefly che- 

 mical, and besides these a slight development of heat takes place, 

 at least in some : but the principal fact is, that a vast quantity of 

 chemical tensions is here stored up, the equivalent of which we 

 again obtain as heat by the combustion of the plants. The only 

 vis viva which we know to be absorbed in the accomplishment of 

 this is that of the chemical solar rays ; we are, however, totally at 

 a loss for the means of comparing the force-equivalents which are 

 thereby lost and gained. Animals present some points in this 

 respect which we can lay hold of. These take in oxygen and 

 the complicated oxidizable combinations which are generated by 

 plants, and give back the same, for the most part burnt, as 

 carbonic acid and water, but in part reduced to simpler com- 

 binations ; hence they consume a certain quantity of chemical 

 tensions, and generate in their place heat and mechanical 



