IDENTICAL LAWS 237 



mentum and of electric charge, the law of gravitation, 

 Maxwell's equations — are not controlling laws.* They 

 are truisms. Not truisms when approached in the way 

 the mind looks out on the world, but truisms when we 

 encounter them in a building up of the world from a 

 basal structure. I must try to make clear our new 

 attitude to these laws. 



Identical Laws. Energy momentum and stress, which 

 we have identified with the ten principal curvatures of 

 the world, are the subject of the famous laws of con- 

 servation of energy and momentum. Granting that the 

 identification is correct, these laws are mathematical 

 identities. Violation of them is unthinkable. Perhaps 

 I can best indicate their nature by an analogy. 



An aged college Bursar once dwelt secluded in his 

 rooms devoting himself entirely to accounts. He realised 

 the intellectual and other activities of the college only 

 as they presented themselves in the bills. He vaguely 

 conjectured an objective reality at the back of it all — 

 some sort of parallel to the real college — though he 

 could only picture it in terms of the pounds, shillings 

 and pence which made up what he would call "the 

 commonsense college of everyday experience". The 

 method of account-keeping had become inveterate habit 

 handed down from generations of hermit-like bursars; 

 he accepted the form of accounts as being part of the 

 nature of things. But he was of a scientific turn and he 

 wanted to learn more about the college. One day in 

 looking over his books he discovered a remarkable law. 



* One law commonly grouped with these, viz. the law of pondero- 

 motive force of the electric field, is not included. It seems to be impos- 

 sible to get at the origin of this law without tackling electron structure 

 which is beyond the scope of our present exercise in world-building. 



