26o PHYSICAL SCIENCE 



observed, no more essentially constant than the 

 value of gold to a mariner when in New York at 

 one time and on a desert island at another. 



Much of our old scheme of science has been 

 put into nature by our own minds, and then redis- 

 covered. Possibly that is why nature has seemed 

 to us to be rational. We are beginning to fear 

 that things too easily rationalised are but the 

 delusive image of ourselves seen in nature's mirror. 

 The real nature may have but little in common 

 with that looking-glass world. Yet one quantity 

 stands out, at present incomprehensible, with all 

 the signs of a real natural constant — the unit of 

 action in Planck's great quantum theory. 



