12 THE LIMITATIONS OF SCIENCE 



tile irony he exposes the absurdity of a materialistic 

 theory derived from mechanics which itself inevitably 

 rests on a purely metaphysical basis. 



According to Rankine, a true physical theory is the 

 most simple system of principles from which the formal 

 laws of phenomena, experimentally discovered, may be 

 deduced. Such a theory resembles a science like 

 geometry in that it originates with definitions and 

 axioms for first principles, and derives their con- 

 sequences logically, by propositions. But, in general, 

 a physical theory differs because these fundamental 

 definitions and axioms discovered first are numerous 

 and complex, since they are deduced from the mass of 

 facts presented to us immediately by nature; whereas 

 the first principles and axioms of geometry are few 

 in number and simple in character, such as a mathe- 

 matical line has length only, and are the results 

 deduced from bodies not necessarily real. In other 

 words, the method pursued in the physical theory is 

 inductive, and is consequently more tentative and 

 laborious than the deductive method of geometry, as 

 the acceptance or rejection of the principles derived 

 must depend upon their agreement with facts dis- 

 covered gradually by observations, and not upon gen- 

 eral properties agreed upon once for all. The proposi- 

 tions of geometry are final, if the axioms and defini- 

 tions are granted; a theory of physics is more or less 

 conjectural, as its first principles are always subject 



