CLASSICAL AND NEW MECHANICS 155 



ably final. But it is inevitable that if we found the 

 laws of light and electricity on mechanics, the time will 

 come when the accumulation of knowledge will in- 

 crease the discrepancies which must always exist be- 

 tween any two branches of science and which will 

 eventually require a thorough revision of one or the 

 other. If the attention be directed more toward dis- 

 covering the phenomena and laws of light and elec- 

 tricity than of mechanics, as it is to-day, these 

 discrepancies will probably be laid to the laws of 

 mechanics and their revision will be attempted to 

 insure agreement. This has occurred in the last few 

 years, and the mechanics based on material bodies is 

 being replaced by a mechanics of electricity or by one 

 of energy, if the terms be permissible. 



The mechanics of material bodies, to which the name 

 of Newton is generally attached, was based on the ob- 

 jective reality of matter, whose quantitative measure 

 was inertia or mass. Newton evidently considered 

 inertia as a fundamental attribute of matter, and thus 

 invariable and inexplicable; something to be accepted 

 and determined solely by experiment. Thus he says 

 in his Principia: " Haec (materiae vis) semper pro- 

 portionalis est suo corpori, neque differt quicquam ab 

 inertia massae, nisi in modo concipiendi. Per inertiam 

 materiae fit, ut corpus omne de statu suo vel quiescendi 

 vel movendi difHculter deterbetur." This postulate may 

 be freely translated to mean that the force of attrac- 



