444 THE SENSORIAL FUNCTIONS. 



that degree of aciiteness of perception, which is 

 best suited to their respective wants and powers 

 of gratification.* 



Chapter VI. 



VISION. 



§ 1. Object of the Sense of Vision. 



To those who study nature with a view to the 

 discovery of final causes, no subject can be more 

 interesting or instructive than the physiology of 

 Vision, the most refined and most admirable of 

 all our senses. However well we may be ac- 

 quainted with the construction of any particular 

 part of the animal frame, it is evident that we 

 can never form a correct estimate of the excel- 

 lence of its mechanism, unless we have also a 

 knowledge of the purposes to be answered by it, 

 and of the means by which those purposes can 

 be accomplished. Innumerable are the works of 

 creation, the art and contrivance of which we 



* The Comparative Physiology of the Voice, a function of 

 which the object, in animals as well as in man, is to produce 

 sounds, addressed to the ear, and expressive of their ideas, feel- 

 ings, desires and passions, forms a natural sequel to that of 

 Hearing ; but Sir Charles Bell having announced his intention 

 of introducing it in his Treatise on the Hand, I have abstained 

 from entering into this extensive subject. 



I 



