vi INTRODUCTION 



subtle minds than the great physicists of the beginning 

 of the nineteenth century had already seen that 

 sensation might mislead us. There was something in 

 us that continually changed — ^that was our conscious- 

 ness, and it was all that we knew. If external things 

 did exist they existed only because we thought them. 

 But we ourselves exist, for we are not only a stream of 

 consciousness that continually changes, but there is in 

 us a personality, or identity, which has remained the 

 same throughout all the vicissitudes of our conscious- 

 ness. If the things that exist for us exist only because 

 we think them, and if we also exist, then we must exist 

 in the thought of an Absolute Mind that thinks us. 

 Physical Science, studying only motions and trans- 

 formations, understood that there was something that 

 moved and transformed — this was matter and energy. 

 Mental Science, studying only thought, understood 

 that nature was only the thought of an Universal 

 Mind. Either conclusion was equally valid Philosophy 

 (or metaphysics), and neither could be proved or dis- 

 proved by the methods of Science. The speculative 

 game is drawn, said Huxley, let us get to practical 

 work ! 



Both Physics and Biology did get to work, with the 

 results that we know. But Physics advanced far 

 beyond the acquirement of the results that stimulated 

 Biology to formulate our present hypotheses of evolu- 

 tion and heredity. As its knowledge accumulated, it 

 began to doubt whether matter and energy, atoms and 

 molecules, mass and inertia — all those things which 

 it thought at first were so real — were anything else 

 after all than ways in which our mental organisation 

 dealt with crude sensations. They might, as Bergson 

 said later on, be the moulds into which we pour our 

 perceptions. Physics set up a test of Reality, the law 



