ANIMALS. 



sight. And thus also, if, instead of two eyes, we 

 had two hundred, we should fancy the objects in- 

 creased in proportion, until one sense had correct- 

 ed the errors of another. 



" The having two eyes might thus be said to 

 be rather an inconvenience than a benefit, since 

 one eye would answer the purposes of sight as 

 well, and be less liable to illusion. But it is 

 otherwise ; two eyes greatly contribute, if not to 

 distinct, at least to extensive vision.* When an 

 object is placed at a moderate distance, by the 

 means of both eyes we see a larger share of it 

 than we possibly could with one ; the right eye 

 seeing a greater portion of its right side, and the 

 left eye of its correspondent side. Thus both 

 eyes, in some measure, see round the object; 

 and it is this that gives it, in nature, that bold 

 relievo, or swelling, with which they appear, and 

 which no painting, how exquisite soever, can 

 attain to. The painter must be contented with 

 shading on a flat surface ; but the eyes, in ob- 

 serving nature, do not behold the shading only, 

 but a part of the figure also, that lies behind 

 these very shadings, which gives it that swelling 

 which painters so ardently desire, but can never 

 fully imitate. 



" There is another defect, which either of the 

 eyes, taken singly, would have, but which is cor- 

 rected by having the organ double. In either eye 

 there is a point which has no vision whatsoever ; 

 so that if one of them only is employed in seeing, 

 there is a part of the object to which it is always 



* Leonardo da Vinci. 



