MAGNETISM. 149 



cal 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 and 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 exist- 

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

 Ley den phial. The old definition of force was, that which 

 caused change in motion ; and yet even this definition pre- 

 sents 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 doubt- 

 ful question, as such absence would involve in this case per- 

 fect 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 

 absolutely 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 of opinion : we have, in support of it, the general 

 facts that magnets do deteriorate in the course of years ; and 

 we have the further general fact of the instability, or fluxional 

 state, of all nature, when we have an opportunity of fairly 

 investigating it at different and remote periods : in many 

 cases, however, the action is so slow that the changes escape 

 human observation, and, until this can be brought to bear 

 over a proportionate period of time, the proposition cannot be 



