MAGNETISM. 133 



line joining the poles, showing apparently that the conducting 

 power of the iron for heat is changed by magnetisation. 



Thus we get heat produced by magnetism and the conduc- 

 tion of heat altered by it in a direction having a definite 

 relation to the direction of the magnetism. Is it necessary to 

 call in aid ether or the substance ' caloric ' to explain these 

 results ? Is it not more rational to regard the calorific effects 

 as changes in the molecular arrangements of the matter sub- 

 jected to magnetism ? 



There is no obvious reason why magnetism, in the dynamic 

 state, i.e. either when the magnet is in motion, or when the 

 magnetic intensity is varying, may not also directly produce 

 chemical affinity and light, though up to the present time such 

 has not been proved to be the case ; the reciprocal effect, also, 

 of the direct production of magnetism by light or heat has 

 not yet been experimentally established. 



I have used, in contradistinction, the terms dynamic and 

 static to represent the different states of magnetism. The 

 applications I have made of these terms may be open to some 

 exception, but I know of no other words which will so nearly 

 express my meaning. 



The static condition of magnetism resembles the static 

 condition of other forces : such as the state of tension existing 

 in the beam and cord of a balance, or in a charged Leyden 

 phial. One of the old definitions of force was, that which 

 caused change in motion ; and yet even this definition presents 

 a difficulty : in a case of static equilibrium, such, for instance, 

 as that which obtains in the two arms of a balance, we get the 

 idea of force without any palpable apparent motion : whether 

 there be really an absence of motion may be a doubtful 

 question, as such absence would involve in this case perfect 

 elasticity, and, in all other cases, a stability which, in a long 

 course of time, nature generally negatives, showing, as I 

 believe, an inseparable connection of motion with matter, and 

 an impossibility of a perfectly immobile or durable state. So 

 with magnetism ; I believe no magnet can exist in an abso- 

 lutely stable state, though the duration of its stability will be 

 proportionate to its original resistance to assuming a polarised 

 condition. This, however, must be taken merely as a matter 



