THE CONSTITUTION OP NATURE. 27 



motion has been augmented by the increase of the dis- 

 tance. These remarks apply to all bodies, whether 

 they be sensible masses or molecules. 



Of the inner quality that enables matter to attract 

 matter we know nothing; and the law of conservation 

 makes no statement regarding that quality. It takes 

 the facts of attraction as they stand, and affirms only 

 the constancy of working-power. That power may ex- 

 ist in the form of MOTION; or it may exist in the form of 

 FORCE, with distance to act through. The former is 

 dynamic energy, the latter is potential energy, the con- 

 stancy of the sum of both being affirmed by the law of 

 conservation. The convertibility of natural forces con- 

 sists solely in transformations of dynamic into poten- 

 tial, and of potential into dynamic energy. In no other 

 sense has the convertibility of force any scientific mean- 

 ing. 



Grave errors have been entertained as to what is 

 really intended to be conserved by the doctrine of con- 

 servation. This exposition I hope will tend to remove 

 them. 



