268 SCIENCE AND THE HUMAN MIND 



a real " thing-in-itself " outside us, resembling in its 

 ultimate character our mental picture of it. 



But what right have we to assume the real existence 

 of such an outside object ? What is it that we really 

 know when we observe the spade ? Nothing, in effect, 

 but impressions on our senses. Our optic nerves send 

 certain stimuli to the brain ; we call them sight of 

 a long brown object with a grey blade. We stretch 

 out our hand and seize the spade. Yet all that 

 we expect, and all that we experience, are certain 

 tactual sensations given to the brain by our sense of 

 touch. 



Chemists have resolved the spade into atoms of 

 carbon, hydrogen, iron, etc. Physicists have gone 

 further, and pictured the atom as a system of whirling 

 electrons. All these attempts to get at a more ulti- 

 mate reality, merely mean that the sensations we 

 experience at first may be changed into others by 

 appropriate action, and that, to represent those new 

 sense-perceptions to our minds, new concepts are 

 needed. By putting the spade into the fire, or by 

 passing an electric discharge through the gases which 

 are thereupon evolved, new phenomena appear, and a 

 new mental scheme is evolved. We cannot anyhow 

 get at the external "thing-in-itself"; we can but 

 modify our sense-impressions and our concepts in 

 certain limited ways. 



Our brain has been likened to a telephone exchange 

 in which the operator sits for ever locked. His only 

 knowledge of the external world is derived from the 

 messages he gets or intercepts as they pass over the 

 wires. He may infer the existence of outside objects, 

 he cannot prove it, and he can only gain a picture of 



