TO THE MOVEMENT OF MACHINES. 11 



31. 



In explanation of the fact that the magneto-electric ciirrents are 

 of a certain duration, great caution must be taken not to adopt 

 that hypothesis which most easily presents itself; for it is veiy 

 rare that such an explanation is con-ect, or even most probable. 

 We shall certainly conclude from it, that some time is required 

 for the soft iron to attain the maximum of magnetic force, or for 

 the development of the magnetism to become any fvmction of 

 the time. The mathematical idea of a force requires that it have 

 an existence independent of time. This is the case with celestial 

 attraction ; as soon as a planet appears opposite to the sun, 

 the force of attraction, in conformity with its actual position, 

 takes place according to the Newtonian law ; no time is necessary 

 for the entire mass of the body to become seized by gravitation. 

 Here is the t\'pe of a force which serves as a basis, if we wish to 

 form a general and cori'ect idea of it. But when a force acts on 

 any system of material points, and if we substitute in place of the 

 primitive effects, the active force this sj^stem has acquired, this 

 latter force will be a fiinction of the time during w hich the action 

 of the force was in operation. This is incontestable, but I think 

 it would not be possible to hazard the inverse conclusion ; for 

 instance, where we perceive the development or the propagation 

 of a force requires time, it is a molecular movement, or the move- 

 ment of any matter taking place. Thus, if we suppose that the 

 development of the magnetism be not instantaneous, we must 

 admit, either that the magnetism consists in the movement of a 

 fluid, or of some aether, or that the magnetic force produces 

 some molecular movement, or positive displacement of the par- 

 ticles of the soft iron. 1 am of the latter opinion ; the time re- 

 quired for the propagation of magnetism being too considerable 

 to allow of attributing this force to the movement of an aether, 

 analogous to the luminous or the electric tether, the rapidity of 

 which, according to Air. Wheatstone's experiments, surpasses 

 even that of light. There is nothing to oppose this, in the sup- 

 position of a positive contraction taking place in the soft iron as 

 soon as it is exposed to magnetic influence. The armature 

 which is attracted by a force equivalent to a weight of 1000 lb.. 

 Mould exercise the same mechanical effects as a weight of the 

 same magnitude attached to an ai'mature of a non-magnetized 

 horse-shoe ; and it is not needful to employ very delicate instru- 

 ments to estimate the compression produced by such a charge. 



