xvi INTRODUCTION 



but we may make an approximation to it ; and we 

 may even hope to get some dim idea of why it has 

 been called into existence, and what is the purpose 

 of its Creator. 



Thus pure science culminates in a Natural 

 Philosophy ; that is, in a philosophy built up on an 

 observational basis, which tries to harmonise and 

 explain all observed facts. And this Natural 

 Philosophy must, of course, vary with our know- 

 ledge, and become more and more precise as that 

 knowledge increases. 1 



The latter half of the nineteenth century will 

 always be memorable for the establishment, by 

 scientific evidence, of the theory of evolution. By 

 which is meant the discovery that the whole 

 Universe is gradually undergoing a progressive 

 change, and that each stage of this progress is the 

 outcome of what went before, and is the cause of 

 what will come after. It is on this foundation that 

 all forms of Natural Philosophy must be built up in 

 the future. 



It was not until the publication of Mr. Darwin's 

 " Origin of Species " that a clear view of evolution 

 was obtained. It was then seen that all animals 

 and plants were genetically related to each other, 

 and that the physical evolution of the solar system 

 had been followed by a biological evolution. When 

 this truth had been firmly established, the inference 



ir lhe term " Natural Philosophy " was formerly limited to 

 the study we now call Physics ; but as this use has been 

 altogether abandoned, I hope that I may be allowed to 

 revert to the still earlier and true meaning of the term. 



