4co Power of Sight limited. [Book IX, 



materially differ in this refpedt, the proper and natural 

 cure is to cover the good eye for fome time j for in 

 this cafe the diftorted eye is obliged to act, and to 

 turn itfelf directly to objects, which in a little time 

 becomes natural and eafy to it. Even a very weak 

 eye acquires ftrength by exercife ; peffbns whofe fquint- 

 ing feemed almoft incurable, having covered their 

 good eye for a few minutes only, have been themfelves 

 furprifed to find the ftrength that their bad eye had 

 acquired by exercife even for that fhort period. When 

 the fquint has proceeded entirely from a vicious habit, 

 a cure has been effected by covering the good eye for 

 a fortnight only *. 



The power? of this fenfe are limited, as well as thofc 

 of every other fenfe and faculty of man. 



i ft. The fight is very limited with refpect to bodies 

 in motion ; for with a certain degree of velocity, as 

 that of a cannon ball through the air, they are not vifi- 

 ble, unlefs very luminous. 



2. The fame effect is exemplified by the experi- 

 ment of whirling a .lighted coal, as was already in- 

 timated. 



3. If two objects unequally diftant more with the 

 iS,me degree of velocity, the more remote will appear 

 the flower. 4th. A vifible object moving with any 

 velocity appears to be at reft, if thf fpace defcribcd 

 in a fecond of time is invifible to the eye. Thus a 

 near object, as the index of a clock, moving flowly, 

 or a remote one, as a planet, moving fwiftly, appears 

 to be at reft. 5th. It is well known, that when the 

 eye is proceeding ftrait forward, as in a boat at fea, a 

 lateral object, either at reft, or moving not fo faft, ap- 

 pears to move the contrary way. 6th. If, however/ 



* Reid's Inquiry 5nTo the Human Mind, p. 253. 



thtf 



