16 THE LIMITATIONS OF SCIENCE 



mechanics are the first principles of the whole science. 

 But they must be employed with great caution and 

 judgment. Their free use tends to confuse the essen- 

 tial differences between hypothesis and fact, between 

 metaphysics and physics, and this confusion does now 

 exist in the minds of the public generally and even in 

 those of many men of science. A desire is, conse- 

 quently, often shown to explain away, or set aside, 

 facts inconsistent with a preconceived hypothesis. 



Such is briefly Rankine's criticism of the prevailing 

 mechanical and materialistic theories of physics. His 

 conclusions are worthy of thoughtful consideration. 

 It has always been the boast of science that by its 

 methods we may avoid the pitfalls in which meta- 

 physical reasoning inevitably ends. Now, if our most 

 elaborate and complete scientific theory is really meta- 

 physical, we must renounce all our proud claims and 

 consider atomic and mechanical theories solely on the 

 grounds of their utility and simplicity. 



A metaphysical hypothesis, valuable solely for its 

 utility, is always dangerous, for by constant use we 

 tend inevitably to give an objective reality to things 

 which in the beginning we knew to exist only in our 

 own minds. And this tendency is especially deplor- 

 able in science, which does little for education if it does 

 not recognize clearly the limits of our knowledge and 

 distinguish accurately between reality and speculation. 



Now the belief in the objective reality of molecules, 



