OF SIGHT. 169 



animals. All those of the lion kind have remarkably large eyes, and 

 all those of the bear kind remarkably small ones ; and the intention of 

 this is very evident ; for we may always know the sphere of motion of 

 the animal in search of its food, or in the common exercise of life, by 

 the size of the eyes. Moles have very small eyes for that reason [in 

 that relation]. This difference is not so much in animals that are 

 always on the surface of the earth, as in birds. 



Civilization appears to have considerable effect on the eyes. Many 

 peojile have sore eyes ; many grow blind. Are the same [effects as 

 common] among savages ? Civilized horses, dogs, &c, are more apt to 

 grow blind than those animals which lead a more natural life, as 

 deer, &c. 



Two toads, after being under ground thirteen months, saw very well 

 on a strong light being let in upon them. 



Vide ' Book of Experiments,' vol. i. p. 84. [Quaere : What Book is 

 this ? — Wm. Cltft. Vol. i. implies another or more. — B. 0.] 



On Squinting. 



Some people squint with one eye only, and never in common vision 

 turn that eye to the object ; it is then commonly turned in towards 

 the nose; but when the other, or active eye, is covered, the affected 

 eye then turns itself towards the object. Other people only squint 

 in some directions of the eye, not in others ; and this is according to 

 the position of the object. If the object be nearly in the direction of 

 the natural position of the [affected] eye, it will find little difficulty in 

 directing its axis towards it. Other people, again, squint with both 

 eyes alternately, respecting the position of the object. Such, I think, 

 find it more difficult to turn the eyes inwards than outwards : they look 

 at the object according as it is placed. If it is a converging squint, 

 they look with the eye which is on the opposite side of the object ; if it 

 is a diverging squint, then the contrary. 



This shows that the squinting eye is not able, or has not been habitu- 

 ated, to turn its axis to all the positions of the head with respect to 

 objects, while the other eye is doing its office ; for, when not under 

 this circumstance, [when compelled to act by itself, the squinting eye] 

 it becomes a good eye. 



On Gutta Serena. 

 The disease called ' gutta serena ' explains the power of motion of the 

 iris, without which we could not form a just idea of it. Every impres- 

 sion [of light on the retina] excites a contracting power in the iris ; 

 which word impression says it is muscular ; but as the iris also dilates, 

 it was not so easy to say whether that was performed by elasticity or 



