THE SCIENTIFIC METHOD 121 



fundamental unit from which the other can be derived. 

 This undoubtedly follows from the fact that we have 

 no conception of matter without energy or of energy 

 without matter. But while it is thus possible mathe- 

 matically to make either of them a starting-point for 

 the explanation of phenomena, the advocates of ener- 

 getics apparently soon develop a pronounced tendency 

 to prefer the abstract to the concrete and to subtilize 

 objective facts into metaphysical ideas. A science like 

 physics, to be useful and not merely an intellectual 

 gymnastics, should preserve in all its speculations a 

 close touch with the practical and the concrete a cer- 

 tain common sense. The history of the science shows 

 these advantages have been obtained most frequently 

 by those who maintain matter and not energy to be 

 a fundamental entity. The failure of the mechanistic 

 school has arisen from the attempt to explain the na- 

 ture of matter, the cause of its forces, and the proper- 

 ties of atoms. However we may try to reason away 

 the belief in the objective reality of matter, our minds 

 persistently cling to the advantage, and even neces- 

 sity, of such a postulate, and we consciously or uncon- 

 sciously endow any substitute of it with all the prop- 

 erties of matter, excepting its name. 



Energy is to be considered then as an attribute of 

 matter and may be defined as the power to do work. 

 It is customary and convenient to divide energy into 

 two classes, potential and kinetic, according as the mat- 



