34 



HABIT AND INTELLIGENCE. 



[chap. 



old-fashioned water-wheel (not a turbine) moves with so 

 small a velocity, that its energy of motion may be regarded 

 as nothing in comparison with the amount of energy of 

 motion that it would attain if it were permitted to fall 

 unobstructed. If, then, the water-wheel is employed in 

 raising weights, the potential energy given out by the 

 descending water is transformed into the potential energy 

 of the raised w^eights, without any intermediate formation 

 of energy of motion. Of course the same kind of trans- 

 formation is possible between the static energy of a raised 

 weight and the static energy of a compressed spring. 



NOTE. 



ELECTRIC AND MAGNETIC ENERGY. 



Electro- 

 dynamic 

 induction. 



Experi- 

 ment I. 



Experi- 

 ment II. 



Explana- 

 tion. 



In this note I intend to give my reasons for believing that 

 electricity and magnetism consist in the straining of molecular 

 elasticities. 



Let two conducting wires, a and B, be placed alongside of 

 each other : or, what is better in many experiments, twisted 

 together into a hollow spiral, but kept from metallic contact by 

 some non-conducting substance. Let an electric current be 

 allowed to flow along a for an appreciable time, and then cut 

 off: on the current beginning to flow along a, a momentary 

 current flows along b in the opposite direction to that along a ; 

 and on the current ceasing to flow along a, another momentary 

 current flows along b in the same direction as that along a.^ 



The most probable interpretation of these facts is, that at the 

 moment when the current begins to flow along a, the molecules 

 of B are thrown into a state of elastic tension : the act of the 

 molecules of B, in assuming the state of tension, constitutes the 

 first current along b ; and the second current (which, as stated 

 above, is in the opposite direction to the first) is constituted by 

 the act of the molecules of b, on the cessation of the current 

 along a, falling back into their normal state. 



^ De la Rive on Electricity, English translation, vol. i. p. 355. 



