72 VISION. 



appropriate organs by those vibrations, should pro- 

 duce, one the sensation called sound, and the other 

 a sensation altogether incomparable with it, namely 

 vision. Neither can we say how it is that the vibra- 

 tions of heat produce a sensation different from 

 either. In short, beyond the sequence made known 

 by experience, we know of no relationship between 

 sonorous, luminous, and thermic vibrations on the 

 one hand, and the sensations of sound, sight, and 

 heat on the other. The sensations may be purely 

 arbitrary consequences of the irritations produced 

 by the various stimuli, for all that science can tell 

 us to the contrary. We perceive in this an instance 

 of the impossibility, in our circumstances, of bridging 

 the gulf between matter and consciousness. 



While, however, the sensations received through 

 the eye, the ear, and the surface of the body, so 

 differ in kind as to be incomparable, they yet 

 combine, by means of the addition of time and 

 space, to give common information. It is ad- 

 mitted that time is an idea independent of the 

 external senses; and, notwithstanding opinions 

 to the contrary, the position is possible that 

 the same is true of space, and that the mind 

 must from the first recognise itself as sur- 

 rounded by non ego as well as existent. How- 

 ever that may be, a sense of the position of the 



