402 THE SENSATIONALIST PHILOSOPHY. 



impression exists ; it seems then reasonable and even necessary to 

 conclude that these depend on a revived similar, but less vivid or less 

 extended action of the nervous system, probably confined to the 

 brain itself. We may be the more confident of this, from knowing as 

 we do, that in some kinds of madness, and in some other forms of 

 disease, which, though affections of the body, extend their influence to 

 the mind, as well as in sleep, the revived sensation or idea may be 

 so vivid as to create belief in an external impression, although none 

 actually exists. Philosophers of this school have found it convenient 

 to use the word idea to express the copy or revival of a sensation such 

 as we have spoken of, and some have deemed it very important to 

 trace the physical action as far as possible. The endeavour to refer 

 the different kinds of mental action to different regions of the brain 

 constitutes the basis of Phrenology, in which effort there has been 

 some apparent success, and as it readily accounts for the different 

 natural mental tendencies and capacities undeniably existing in differ- 

 ent individuals, there might possibly have been much more complete 

 success, if anatomical examination and patient observation of facts had 

 been aided by juster views of the general laws of mind and the proper 

 distinction of its so called faculties. We must not now, however, pur- 

 sue this branch of the subject. 



Dr. Hartley attempted the examination of the physical action intrO" 

 ducing sensations with the best lights his age afforded, and concluded 

 that there was reason to believe the nervous action to be vibratory. 

 He consequently spoke of sensations as depending on vibration, whilst 

 to express the less vivid or less extended action which he regarded as 

 the corresponding physical cause of the ideas or revivals of sensations 

 he invented the term vibratiuncles or lesser vibrations. 



His object was to bring out strongly the relation between the sen- 

 sations and their revivals, and thence the possibility that a principle 

 of physical sympathy, strictly analogous with other known facts 

 respecting the human frame, would explain and confirm the observed 

 law according to which ideas are produced. The particular kind of 

 action supposed was of no real importance to the theory — but, in truth, 

 the objections commonly made to Hartley's explanation were drawn 

 from strange perversions of his meaning by those who had never taken 

 the trouble to study his statements. Think, for example, of men pre- 

 tending to philosophy, ridiculing him for representing the nerves as 

 acted upon like strings under tension, for which notion he never gave 



