SOME FORCES OF THE SOCIAL ORGANISM. 509 



So soon as the motion ceases the force is gone. But it is most 

 important to notice that no power need be exerted by the engine 

 to call forth a manifestation of electro-motive force, because there 

 is not as yet any appreciable opposition to the rotation of the 

 armature. 



Third. The instant the free ends of the armature wires are 

 joined, the attraction, or potential as it is called, diminishes, a 

 current of electricity rushes through the wire, and the mysteri- 

 ous opposition to rotation at once springs into existence, the belt 

 grows taut on the driving side, the engine takes more steam and 

 labors harder and harder, while a constant stream of mechanical 

 power must be supplied by it to the dynamo to maintain that mo- 

 tion which a minute before went on so easily and freely. 



The electrical current passing out from the dynamo is con- 

 stantly carrying energy away from it. This loss must be inces- 

 santly supplied by the steam engine, and this demand is brought 

 about by the opposition to rotation set up within the machine 

 through reaction of the electro-motive force on the material of 

 the conductor and on the magnetic lines. Thus we have here the 

 constant characteristic of a closed system where invariably the 

 product of a reaction opposes the primitive cause of the change. 



Thus far the phenomena just quoted exemplify the rule. It 

 would not have been worth while to take so much time to describe 

 the dynamo if nothing more was to be learned from it, but there 

 is. This semi-living machine, whose elements are so simjDle com- 

 pared with those of a really living structure, enables us, because of 

 its mechanical simplicity, to go one step further in our analysis 

 and to inquire how the result of the change reacts on the exciting 

 cause. It is known beyond doubt that in a working dynamo the 

 action of the current is twofold. It not only tends to stop the 

 armature, but it actually diminishes the magnetism of the fields, 

 and so lessens the electro-motive force by attacking it at the very 

 place of its origin. Let me repeat : the magnetism and the rota- 

 tion create the electro-motive force ; this latter creates the cur- 

 rent ; then the current in turn reacts both to oppose the rotation 

 and to cut down its own initial cause ; and, further, this reaction 

 on the cause is found always to require an appreciable time. 



Here, I think, we have struck a new principle. In electrical 

 matters it has been known only a few years, and has had no ap- 

 plications in other sciences, but I venture to think it is somewhat 

 general, and that illustrations of it may be found elsewhere, one 

 or two of which I will endeavor to submit. 



A spiral spring supporting a weight does not manifest this 

 principle, for the cause that is, the weight is not lessened by 

 the pressure it produces. The same is true of all static states ; but 

 when motion occurs, then this new principle may often be observed. 



