12 THE FOUNDATIONS OF SCIENCE 



with the living organisms as a whole, where green 

 first becomes visible, we come on a new factor, the 

 tremendous factor of life. Comparative physiology 

 introduces us to different types of animals and plants, 

 which are studied from another point of view in the 

 almost pure green of the natural history of the 

 zoologist and field botanist. 



In contact with all the biological section devoted 

 to animals, and perhaps just touching that concerned 

 with plants, blue becomes visible in our diagram, 

 and we find once more a new phenomenon, which 

 transcends mere life as life transcends lifeless matter 

 the phenomenon of mind and consciousness. Here 

 we enter psychology, that study of mind which is 

 of immemorial antiquity on the one side of intro- 

 spection, and is of the newest group of sciences on 

 the other, as a matter of experimental observation. 

 It touches physiology most closely of the biological 

 sciences, so that physiology, which comes in contact 

 with chemistry and physics, must be pictured in our 

 diagram as a region of space running across the whole 

 of that portion of the triangle given up to biology. 



From psychology we pass to the theory of know- 

 ledge, and thus we complete the circuit of our figure. 

 We find ourselves once more at our starting-point of 

 logical principles, which, on one side, have affinities 

 with psychology, since they are apprehended by the 

 direct action of our minds, and on the other are the 

 basis of physics and all other sciences. 



