of Physical Knowledge. 63 



organism, whose separate parts fit together so intimately that 

 any interference at one place is felt in various other places, 

 sometimes far removed. Wherefore, since every conclusion 

 of theory results from the cooperation of several theorems, 

 it follows that, as a rule, several theorems may be made 

 responsible for each failure of the theory, and there are 

 generally several possibilities of finding the way out. 

 Usually, the question is eventually reduced to a conflict 

 between two or three propositions which hitherto have found 

 a place in the theory, but of which one must be abandoned 

 in face of the new fact. The conflict lasts often for years or 

 decades ; and its final decision not only means the destruction 

 of the defeated theorem, but also quite naturally — and this 

 is specially important — a corresponding confirmation and 

 elevation of the victorious constituent theorems which 

 survive. 



And now we must note the extremely important and 

 remarkable result that in all this war and conflict it is just 

 the great Physical Principles which have held the field, — such 

 as the Principle of the Conservation of Energy, the Principle 

 of the Conservation of Momentum, the Principle of Least 

 Action, and the chief laws of Thermodynamics. Their 

 importance has thus been considerably increased ; while, on 

 the other hand, the theorems which have succumbed in the 

 fight are those on which theoretical developments were based 

 tacitly, either because they seemed so self-evident that it was 

 not, as a rule, considered necessary to mention them, or because 

 they were forgotten. In general, then, one may assert that the 

 most recent development of theoretical physics is marked by 

 the victory of the great Physical Principles over certain 

 deeply-rooted and yet merely habitual assumptions and 

 conceptions. 



To illustrate these statements, I may adduce some of 

 those theorems which have hitherto been used without any 

 hesitation as the self-evident foundations of any theory, but 

 which, in the light of new facts, have proved untenable, or 

 extremely doubtful, in face of the general principles of 

 Physics. I mention three : The Invariability of Chemical 

 Atoms ; The Mutual Independence of Space and Time ; and 

 The Continuity of all Dynamical Effects. 



Of course it is not my intention here to quote all the 

 important arguments which tell against the Invariability of 

 Chemical Atoms. I shall only mention the single fact which 

 brought about an inevitable conflict between this assumption 

 — formerly always regarded as self-evident — and a general 

 physical principle. The fact is the constant evolution of 



