SELECTIVE INFLUENCE OF THE MIND 239 



of that which is obeying it. We can measure certain 

 forms of energy with a thermometer, momentum with 

 a ballistic pendulum, stress with a manometer. Com- 

 monly we picture these as separate physical entities 

 whose behaviour towards each other is controlled by 

 a law. But now the theory is that the three instruments 

 measure different but slightly overlapping aspects of a 

 single physical condition, and a law connecting their 

 measurements is of the same tautological type as a "law" 

 connecting measurements with a metre-rule and a foot- 

 rule. 



I have said that violation of these laws of conserva- 

 tion is unthinkable. Have we then found physical laws 

 which will endure for all time unshaken by any future 

 revolution? But the proviso must be remembered, 

 "granting that the identification [of their subject 

 matter] is correct". The law itself will endure as long 

 as two and two make four; but its practical importance 

 depends on our knowing that which obeys it. We 

 think we have this knowledge, but do not claim in- 

 fallibility in this respect. From a practical point of view 

 the law would be upset, if it turned out that the thing 

 conserved was not that which we are accustomed to 

 measure with the above-mentioned instruments but 

 something slightly different. 



Selective Influence of the Mind. This brings us very 

 near to the problem of bridging the gulf between the 

 scientific world and the world of everyday experience. 

 The simpler elements of the scientific world have no 

 immediate counterparts in everyday experience; we 

 use them to build things which have counterparts. 

 Energy, momentum and stress in the scientific world 

 shadow well-known features of the familiar world. 



