236 Prof. Faraday on the Consewation of Force. 



tricity and magnetism, we find great latitude of assumption ; 

 and necessarily so, for the powers become more and more com- 

 plicated in their conditions. But still there is no apparent desire 

 to let loose the force of the principle of conservation, even in 

 those cases where the ajipearance and disappearance of force may 

 seem most evident and striking. Electricity appears when there 

 is consumption of no other force than that required for friction ; 

 we do not know how, but we search to know, not being willing 

 to admit tliat the electric force can arise out of nothing. The 

 two electricities are developed in equal proportions ; and having 

 appeared, we may dispose variously of the influence of one upon 

 successive portions of the other, causing many changes in rela- 

 tion, yet never able to make the sum of the force of one kind in 

 the least degree exceed or come sho-j't of the sum of the other. 

 In that necessity of equality we see another direct proof of the 

 conservation of force, in the midst of a thousand changes that 

 require to be developed in their principles before we can consider 

 this part of science as even moderately known to us. 



One assumption with regard to electricity is, that there is an 

 electric fluid rendered evident by excitement in plus and minus 

 proportions. Another assumption is, that there are two fluids of 

 electricity, each particle of each repelling all particles like itself, 

 and attracting all particles of the other kind always, and with a 

 force proportionate to the inverse square of the distance, being 

 so far analogous to the definition of gravity. This liypothesis is 

 antagonistic to the law of the conservation of force, and open to 

 all the objections that have been, or may be, made against the 

 ordinary definition of gravity. Another assumption is, that each 

 particle of the two electricities has a given amount of power, and 

 can only attract contrary particles with the sum of that amount, 

 acting upon each of two with only half the power it could in like 

 circumstances exert upon one. But various as are the assump- 

 tions, the conservation of force (though wanting in the second) 

 is, I think, intended to be included in all. I might repeat the 

 same observations nearly in regard to magnetism, — whether it be 

 assumed as a fluid, or two fluids or electric currents, — whether the 

 external action be supposed to be action at a distance, or depend- 

 ent on an external condition and lines of force — still all are in- 

 tended to admit the conservation of power as a principle to which 

 the phseuoraena are subject. 



The principles of physical knowledge are now so far developed 

 as to enable us not merely to define or describe the knoion, but 

 to state reasonable expectations regarding the unknozvn ; and I 

 think the princi])le of the conservation of force may greatly aid 

 experimental philosophers in that duty to science, which consists 

 in the enunciation of problems to be solved. It will lead us, in 



