258 SENSATION AND THE SENSIFEROUS OKGANS. 



Hartley, like Haller, had no conception of the nature 

 and functions of the grey matter of the brain. But, if 

 for " white medullary substance," in the latter paragraph, 

 we substitute " grey cellular substance," Hartley's propo- 

 sitions embody the most probable conclusions which are 

 to be drawn from the latest investigations of physiolo- 

 gists. In order to judge how completely this is the case, 

 it will be well to study some simple case of sensation, 

 and, following the example of Reid and of James Mill, 

 we may begin with the sense of smell. Suppose that I 

 become aware of a musky scent, to which the name of 

 " muskiness " may be given. I call this an odour, and I 

 class it along with the feelings of light, colours, sounds, 

 tastes, and the like, among those phenomena which are 

 known as sensations. To say that I am aware of this 

 phenomenon, or that I have it, or that it exists, are 

 simply different modes of affirming the same facts. If I 

 am asked how I know that it exists, I can only reply that 

 its existence and my knowledge of it are one and the 

 same thing ; in short, that my knowledge is immediate 

 or intuitive, and, as such, is possessed of the highest con- 

 ceivable degree of certainty. 



The pure sensation of muskiness is almost sure to bo 

 followed by a mental state which is not a sensation, but a 

 belief, that there is somewhere close at hand a something 

 on which the existence of the sensation depends. It may 



those of Hartley ; and they appear to have originated independently, though 

 the"Essai dc Psychologic " (1754) is of five years' later date than the 

 " Observations on Man" (1749). 



