226 Prof. Faraday on the Conservation of Force. 



as regards the principle of conservation, but simply, that being, 

 as far as we perceive, inconvertible in its nature and unchange- 

 able iu its manifestation, it oflfers an unchanging test of the 

 matter which we recognize by it. 



Agreeing with those who admit the conservation of force to 

 be a principle in physics as large and sure as that of the inde- 

 structibility of matter, or the invariability of gravity, I think 

 that no particular idea of force has a right to unlimited or un- 

 qualified acceptance that does not include assent to it ; and also 

 to definite amount and definite disjjosition of the force, either in 

 one effect or anothei", for these are necessary consequences ; 

 therefore I urge that the conservation of force ought to be ad- 

 mitted as a physical principle iu all our hypotheses, whether 

 partial or general, regarding the actions of matter. I have had 

 doubts in my own miud whether the considerations I am about 

 to advance are not rather metaphysical than physical. I am 

 unable to define what is metaphysical in physical science ; and 

 am exceedingly adverse to the easy and unconsidered admission 

 of one supposition upon another, suggested as they often are by 

 very imperfect induction from a small number of facts, or by a 

 very imperfect observation of the facts themselves ; but, on the 

 other hand, 1 think the philosopher may be bold in his applica- 

 tion of principles which have been developed by close inquiry, 

 have stood through much investigation, and continually increase 

 in force. For instance, time is growing up daily into importance 

 as an element in the exercise of force. The earth moves in its 

 orbit in time ; the crust of the earth moves in time ; light moves 

 in time ; an electro-magnet requires time for its charge by an 

 electric current : to inquire, therefore, whether power, acting 

 either at sensible or insensible distances, always acts in time, is 

 not to be metaphysical ; if it acts iu time and across space, it 

 must act by physical lines of force ; and our view of the nature 

 of the force may be affected to the extremest degree by the con- 

 clusions which experiraeut and observation on time may supply, 

 being perhaps finally determinable only by them. To inquire 

 after the possible time in which gravitating, magnetic, or electric 

 force is exerted, is no more metaphysical than to mark the times 

 of the hands of a clock in their progress ; or that of the temple 

 of Serapis in its ascents and descents ; or the periods of the 

 occultations of Jupiter's satellites; or that in which the light 

 from them comes to the earth. Again, in some of the known 

 cases of action in time, something happens whilst the ^ime is 

 passing which did not happen before, and does not continue 

 after ; it is therefore not metaphysical to expect an effect in eve/y 

 case, or to endeavour to discover its existence and determine its 

 nature. So in regard to the principle of the conservation of 



