NATURAL PHILOSOPHY. 179 



ation, 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 

 consequences ; but none should oppose or contradict it. 



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

 tion, though it may not contradict the principle, cannot be accepted as suf- 

 ficient or complete unless the former be contained in it ; that however well 

 or perfectly the definition may include and represent the state of things com- 

 monly 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 there- 

 fore cannot be considered as representing its whole nature ; that, indeed, it 

 may express only a very small part of the whole, only a residual phenome- 

 non, and hence give us but little indication of the full natural truth. Allow- 

 ing the principle 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 hypothesis, 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 

 examination, for there lies the hope of a discovery of new laws or a new con- 

 dition of force. The deficiency should never be accepted as satisfactory, but 

 be remembered and used as a stimulant to further inquiry; for conversions 

 offeree may here lie hoped for. Suppositions maybe 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 suppo- 

 sition, if made, must be consistent with the nature of the original hypothe- 

 sis, and may, therefore, by the application of experiment, be converted into 

 a farther test of probable truth. The case of a force simply removed or sus- 

 pended, without a transferred exertion in some other direction, appears to 

 me to be absolutely impossible. 



If the principle be accepted as true, we have a right to pursue it to its con- 

 sequences, no matter what they may be. It is, indeed, a duty to do so. A 

 theory may be perfection, as far as it goes, but a consideration going beyond 

 it, is not for that reason to be shut out. We might as well accept our 

 limited horizon as the limits of the world. No magnitude, either of the 

 phenomena or of the results to be dealt with, should stop our exertions to 

 ascertain, by the use of the principle, that something remains to be dis- 

 covered, and to trace in what direction that discovery may lie. 



I will endeavor to illustrate some of the points which have been urged, by 

 reference, in the first instance, to a case of power, which has long had great at- 

 tractions for me, because of its extreme simplicity, its promising nature, its 

 universal presence, and its invariability under like circumstances ; on which, 



