ORGANS OF PERCEPTION. 165 
wression 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 which I have ventured 
to add Heat. 
When an impression is produced onany 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speedily withdrawn from the excited organ, our notions of its 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 m- 
