1857.] on the Conservation of Force. 863 



exert upon one. But various as are the assumptions, the conserva- 

 tion 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 dependent on an external condition 

 and lines of force — still all are intended to admit the conservation 

 of power as a principle to which the phenomena are subject. 



The principles of physical knowledge are now so far developed 

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

 state reasonable expectations regarding the unknown ; and I think 

 the principle of the conservation of force may greatly aid experi- 

 mental philosophers in that duty to science, which consists in the 

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

 where the force remaining unchanged in form is altered in direction 

 only, to look for the new disposition of the force ; as in the cases 

 of magnetism, static electricity, and perhaps gravity, and to ascer- 

 tain that as a whole it remains unchanged in amount : — or, if the 

 original force disappear, either altogether or in part, it will lead us 

 to look for the new condition or form of force which should result, 

 and to develope its equivalency to the force that has disappeared. 

 Likewise, when force is developed, it will cause us to consider the 

 previously existing equivalent to the force so appearing ; and many 

 such cases there are in chemical action. When force disappears, 

 as in the electric or magnetic induction after more or less discharge, 

 or that of gravity with an increasing distance ; it will suggest a 

 research as to whether the equivalent cliange is one within tlie 

 apparently acting bodies, or one external (in part) to tjiem. It 

 will also raise up inquiry as to the nature of the internal or external 

 state, both before the change and after. If supposed to be external, 

 it will suggest the necessity of a physical process, by which the 

 power is communicated from body to body ; and in the case of 

 external action, will lead to the inquiry whether, in any case, there 

 can be truly action at a distance, or whether the ether, or some 

 other medium, is not necessarily present. 



We are not permitted as yet to see the nature of the source of 

 physical power, but we are allowed to see much of the consistency 

 existing amongst the various forms in which it is presented to us. 

 Thus if, in static electricity, we consider an act of induction, we can 

 perceive the consistency of all other like acts of induction with it. 

 If we then take an electric current, and compare it with this induc- 

 tive effect, we see their relation and consistency. In the same 

 manner we have arrived at a knowledge of the consistency of mag- 

 netism with electricity, and also of chemical action and of heat 

 with all the former ; and if we see not the consistency between 

 gravitation with any of these forms of force, I am strongly of tlie 

 mind that it is because of our ignorance only. How imperfect 

 would our idea of an electric current now be, if we were to leave 



Vol. II. 2 c 



