422 Sevfation and Perception. [Book X. 



tion exprefles that knowledge we obtain^ by means of 

 our fenfations of the qualities of matter *. 



f Senfations may be communicated from without ; 

 i ft. by actual contact witli the object itfelf ; idly, by 

 the intervention of fome medium ; and it amounts 

 to the fame, whether we perceive the qualities of 

 bodies by a communication with the bodies them- 

 felves, or by the effects which they uniformly produce 

 on fome medium which communicates with our fenfes. 

 Thus, when we fee a body white, we do not fay that the 

 light is perceived by our fenfes, but the whitenefs of 

 the body, or that property in the body which fo dif- 

 pofes the rays of light as to afford us the perception 

 or idea of white J. When, therefore, we fpeak of 

 fmells, taftes, colours, founds, we mean that certain 

 effects are uniformly wrought upon our fenfes in cer- 

 tain 



Outlines of Mor. Phil. p. 21, 22. 



f The different fenfes by whofe operation we difcern the qua- 

 lities of external objefls, have been already ftated to be five in 

 number. Touching, tafting, fmelling, hearing, and fight. They 

 may perhaps all be refolved into that of feeling ; yet the dif- 

 tinftion is correcl, as they are certainly different inftruments of 

 feeling or perception. In thofe of touching and tafte an aftual 

 contact with the body, which is the objeft of the fenfe, is requifite. 

 In the others the fenfation is effected through the operation of fome 

 medium. Tii;s fight is in reality the effect of the rays of light 

 upon our optic nerve; found is a vibration of the air, which 

 afrecb the organs of hearing ; and fmell depends upon the ema- 

 nation of certain particles from a body, which aft upon the organ 

 of fcent. 



That fome fenfes are more acute in certain animals than in others, 

 is an obvious faft. The power of fmelling in fome of the canine 

 fpecies is beyond any thing that we are able to conceive. Cats and 

 owls have undoubtedly a power of feeing with a much fmaller 

 portion of light than any human being. It is probable that in 

 different men fome fenfes may be more acute than others. 



J There is undoubtedly fomething in objects which excites fen- 

 fations, but ths fenfations themfelves cannot exift without a fubjeft 



