ORGANS OF PKHCKPTIOX. 1 65 



upon the tongue or the fingers, indicating their pre- 

 sence, while they act with energy on the eye. The vibra- 

 tions of the air make no impression on the eye, the mouth, 

 or the nose, while they instantly act upon the ear. Sensa- 

 tion, therefore, is a generic term, intimating the capability 

 of the nervous system to receive impressions of exter- 

 nal objects ; and it includes as many species as there are 

 impressions calculated to act on one organ, and not upon 

 another, distinguished by this common property, that they 

 intimate the presence of objects. 



The number of impressions which may be regarded as 

 distinct species, is more extensive than is generally imagin- 

 ed, and would justify us in considering the term Sensation 

 as the index of an order or class, rather than of a subordi- 

 nate division. Philosophers, however, have agreed to re- 

 duce our sensations to five kinds, namely, those of Touch, 

 Sight, Hearing, Taste, and Smell, to wliich I have ventured 

 to add Heat. 



When an impression is produced on any one of these senses, 

 there is an intimation given to the mind, of the presence of an 

 object with which that sense is more immediately connected. 

 Thus, the sense of touch warns us of the contact of a body 

 with our skin. Taste, smell, hearing, sight, and heat, of the 

 presence of sapid, odorous, sonorous, luminous, and calorific 

 bodies. The first impression of an object on the senses, con- 

 veys, therefore, little information, except that of presence or 

 existence ; and if the body producing the impression, be ' 

 speedily withdrawn from the excited organ, our notions of its 

 character will be very imperfect. But, if the object conti- 

 nues to act upon our-sense, we begin to analyze the impres- 

 sion. By comparing it with some former impression, we dis- 

 cover the extent of resemblance or diversity ; and, by vary- 

 ing the condition of the object, or the sense directed to it, we 

 attempt to discover the circumstances, which give to the im~ 



