The Domain of Physical Science 213 



nature in virtue of mathematical identities ; but he can also find 

 other entities which obey laws unknown in nature. It is not 

 the basal structure but the principle of selection which plays 

 the all-important part in determining whether a law such as the 

 conservation of energy shall take rank as a law of nature. 



This principle of selection is partly determined by the funda- 

 mental idea of the external world that it shall embody the common 

 element of the experiences of individuals in all possible circum- 

 stances. Therefore those entities or symbolic combinations which 

 give greater weight to the experience of one individual rather than 

 another cannot be allowed to appear in it. But after this sifting 

 a further selection is necessary. It has already been stated that 

 physics is content to take as standard the presentation to a normal 

 intelligence, and it does not carry the symposium of appearances 

 further. The selection thus ultimately depends on the contact 

 of normal human consciousness with the physical world ; certain 

 entities outside us awake directly or indirectly a response in our 

 consciousness, and these thereby enter into the subject-matter ot 

 physics. Other entities equally substantial in their own right 

 awake no response in consciousness ; no mental pictures vivify 

 them ; they are left out of the subject-matter of physics and 

 degraded to the level of curious constructs of the mathematician. 



The principle of selection followed by the mind appears to be 

 primarily a search for the things which are perrnanent. Just as 

 the eye ranging over the ocean takes no notice of the changing 

 motions of the particles of water but fastens attention on the steadily 

 advancing wave-form, so the mind in its contact with nature 

 ignores the more changeable entities but clothes with a vivid sub- 

 stantiality the things which endure. When we find that a number 

 of the laws of nature take the form that such and such entities are 

 permanent (or in scientific language that there is a law of conserva- 

 tion of mass, energy, momentum, electric charge, etc.), it is fairly 

 safe to say that such laws are due to the mind in this sense. There 

 is no law of government in the external world tending to preserve 

 unchanged specially created entities which occupy it ; but the 

 mind has by diligent search picked out the possible constructs 

 which have this permanence in virtue of their mode of construc- 

 tion, and by giving value to these and neglecting the rest has 

 imposed a law of conservation of the things of value. On the other 

 hand, the mind itself may have (jleveloped this tendency through 



