SCIENTIFIC MATERIALISM. 119 



a definite molecular condition of motion or structure is set 

 up in the brain ; or who would be disposed even to deny 

 that if the motion or structure be induced by internal 

 causes instead of external, the effect on consciousness will 

 be the same ? Let any nerve, for example, be thrown by 

 morbid action into the precise state of motion which would 

 be communicated to it by the pulses of a heated body, 

 surely that nerve will declare itself hot — the mind will 

 accept the subjective intimation exactly as if it were ob- 

 jective. The retina may be excited by purely mechanical 

 means. A blow on the eye causes a luminous flash, and 

 the mere pressure of the finger on the external ball pro- 

 duces a star of light, which Newton compared to the circles 

 on a peacock's tail. Disease makes people see visions and 

 dream dreams ; but, in all such cases, could we examine 

 the organs implicated, we should, on philosophical grounds, 

 expect to find them in that precise molecular condition 

 which the real objects, if present, would superinduce. 



The relation of physics to consciousness being thus 

 invariable, it follows that, given the state of the brain, the 

 corresponding thought or feeling might be inferred ; or 

 given the thought or feeling, the corresponding state of the 

 brain might be inferred. But how inferred ? It would be 

 at bottom not a case of logical inference at all, but of 

 empirical association. You may reply that many of the 

 inferences of science are of this character ; the inference, 

 for example, that an electric current of a given direction 

 will deflect a magnetic needle in a definite way ; but the 

 cases differ in this, that the passage from the current to tin- 

 needle, if not demonstrable, is thinkable, and that we enter- 

 tain no doubt as to the final mechanical solution of the 

 problem. But the passage from the physics of the brain 

 to the corresponding facts of consciousness is unthinkable. 

 Granted that a definite thought, and a definite molecular 

 action in the brain occur simultaneously ; we do not possess 





