Prof. Faraday on the Conservation of Force. 227 



force, I do not think that to admit it and its consequences, 

 whatever they may be, is to be metaphysical ; on the contraiy, 

 if that word have any apphcation to physics, then I think that 

 any hypothesis, whether of heat, or electricity, or gravitation, or 

 any other form of force, which either wittingly or unwittingly 

 dispenses with the principle of conservation, is more liable to 

 the charge than those which, by including it, become so far 

 more strict and precise. 



Supposing that the truth of the principle of the conservation 

 of force is assented to, I come to its uses. No hypothesis should 

 be admitted, nor any assertion of a fact credited, that denies the 

 principle. No view should be inconsistent or incompatible with 

 it. Many of our hypotheses in the present state of science may 

 not comprehend it, and may be unable to suggest its conse- 

 quences, but none should oppose or contradict it. 



If the principle be admitted, we perceive at once that a theory 

 or definition, though it may not contradict the principle, cannot 

 be accepted as sufficient or complete unless the former be con- 

 tained in it ; that however well or perfectly the definition may 

 include and represent the state of things commonly considered 

 under it, that state or result is only partial, and must not be 

 accepted as exhausting the power or being the full equivalent, 

 and therefore cannot be considered as representing its ivhole 

 nature; that, indeed, it may express only a very small part of 

 the whole, only a residual phsenomenon, and hence give us but 

 little indication of the full natural truth. Allowing the prin- 

 ciple its force, we ought in every hypothesis either to account 

 for its consequences, by saying what the changes are when force 

 of a given kind apparently disappears, as when ice thaws, or else 

 should leave space for the idea of the conversion. If any hypo- 

 thesis, more or less trustworthy on other accounts, is insufficient 

 in expressing it or incompatible with it, the place of deficiency 

 or opposition should be marked as the most important for exami- 

 nation, for there lies the hope of a discovery of new laws or a 

 new condition of force. The deficiency should never be accepted 

 as satisfactory, but be remembered and used as a stimulant to 

 further inquiry ; for conversions of force may here be hoped for. 

 Suppositions may be accepted for the time, provided they are 

 not in contradiction with the principle. Even an increased or 

 diminished capacity is better than nothing at all ; because such 

 a su])position, if made, must be consistent with the nature of 

 the original hypothesis, and may therefore, by the application of 

 ex]){'riiiicnt, be converted into a further test of probable truth. 

 The case of a force sim])ly removed or suspended, without a 

 transferred exertion in some other direction, appears to me to be 

 absolutely impossible. 



R2 



