(52 FRAGMENTS OF SCIENCE 



tance between the attracting bodies, while, in the other 

 case, the power of producing motion has been augmented 

 by the increase of the distance. These remarks apply to 

 all bodies, whether they be sensible masses or molecules. 

 Of the inner quality that enables matter to attract mat- 

 ter 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 exist in the form of 

 MOTION; or it may exist in the form of FORCE, with dis- 

 tance to act through. The former is dynamic energy, the 

 latter is potential energy, the constancy of the sum of both 

 being affirmed by the law of conservation. The converti- 

 bility of natural forces consists solely in transformations 

 of dynamic into potential, and of potential into dynamic, 

 energy. In no other sense has the convertibility of force 

 any scientific meaning. 



Grave errors have been entertained as to what is really 

 intended to be conserved by the doctrine of conservation. 

 This exposition I hope will tend to remove them. 



