1 8 Presidential Address 



closer and more exact knowledge that 

 has led to the kind of scientific scepticism 

 now referred to ; and that the simple laws 

 on which we used to be working were thus 

 simple and discoverable because the full 

 complexity of existence was tempered to 

 our ken by the roughness of our means of 

 observation. 



Kepler's laws are not accurately true, 

 and if he had had before him all the data 

 now available he could hardly have dis- 

 covered them. A planet does not really 

 move in an ellipse but in a kind of hypo- 

 cycloid, and not accurately in that either. 



So it is also with Boyle's law, and 

 the other simple laws in Physical Chem- 

 istry. Even Van der Waals' general- 

 isation of Boyle's law is only a further 

 approximation . 



In most parts of physics simplicity has 

 sooner or later to give place to complexity: 

 though certainly I urge that the simple 

 laws were true, and are still true, as far 

 as they go, their inaccuracy being only 

 detected by further real discovery. The 

 reason they are departed from becomes 



