186 THE PRINCIPLES OF SCIENCE 



hoc contrivance, this "particle" was purposively designed to be the 

 undetected, and then undetectable, vehicle for the con\Tyance of 

 energy from experimental systems in which the conservation law 

 ( and others of its kind ) apparently fail. 



Some two centuries ago, close to the beginning of this \^ery complex 

 development, its leitmotif was voiced by Bernoulli in a statement 

 which echoes Democritus : 



To try to demonstrate this law would be to obscure it. Indeed, every- 

 one regards this as an incontestable axiom, that an efficient cause 

 cannot perish, either as a whole or in part, without producing an 

 effect equal to its loss. 



That axiom being held incontestable, we have throughout pursued 

 an elusive constancy in the absolute conviction that some such con- 

 stancy exists. Thus, as Meyerson emphasizes, we have perfectly con- 

 sistently multiplied species of energies if and as required for con- 

 stancy of "energy." 



The quest for continuity we hsive found so imperious, and so highly 

 profitable, here yields a conservation principle like all other conser\^a- 

 tion principles. By dint of conceptual invention and empirical dis- 

 covery, at last we reveal— underlying even the most drastic change- 

 one perfect invariance. Invariance in hand, we now sense within 

 reach that incomparably satisfying absolute continuity we call iden- 

 tity. But here, alas, what remains identical is an exceedingly abstract 

 "essence" difficult to conceive and, if Poincare is right, impossible to 

 define. 



In each particular case it is clearly seen what energy is and at least 

 a provisional definition of it can be given; but it is impossible to find a 

 general definition for it. 



If we try to enunciate the [conservation] principle in all its gen- 

 erality and apply it to the universe, we see it vanish, so to speak, and 

 nothing is left but this: There is something which remains constant. 



The conservation principle is then an incomplete consummation of 

 the quest for absolute identity in nature, which, however, we can 

 pursue in another direction. This particular pursuit is indeed perhaps 

 the most ancient and compelling effort spawned by the principle of 

 continuity, and also one to which modern science owes much of its 

 cachet. W'e sacrifice continuity in space to gain a perfectly genuine 

 identity in time. 



