383 



I see both legs with medium distinctness at the distance of 10 

 inches. 



At the distance of about 8% inches I see the two oblique 

 lines equally well, but not so distinctly as at the distance of 10 

 inches. 



At the distance of 1 2 inches I see the two oblique lines with much 

 about the same distinctness as that with which I see them at the 

 distance of 8^ inches. 



It thus appears that I cannot see either of the oblique lines with 

 perfect distinctness and definition at any distance ; but that I can 

 see them both simultaneously distinctly enough at any distance from 

 8^ inches to 12. At a nearer distance than 8| inches, or a further 

 distance than 1 2 inches, the distinctness diminishes, and that equally 

 for the two lines. 



I cannot by any adjustment of my eyes vary the distinctness with 

 which I see the oblique lines at a given distance. 



The preceding analysis of my sight shows that my eyes are not 

 monostigmaticy that is, are not capable of collecting all the rays of 

 light which enter them to one exact focus. It shows, on the contrary, 

 that my eyes are distigmatic, that is, they have each two distinct 

 foci to which they bring the rays, viz. one focus for horizontal rays, 

 and one for vertical rays. 



The preceding analysis also shows that my eyes do not possess any 

 intrinsic power of adjustment whereby they can bring to foci rays 

 diverging from a nearer or further distance than the two distances 

 above specified for horizontal and for vertical rays. 



It is true that I can see the different objects in a room distinctly 

 enough without the aid of glasses, and that in the street or open 

 country I can see objects distinctly enough for all practical purposes 

 with the aid of concave glasses Nos. 2 and 3, but, critically speaking, 

 the definition is far from being exact. 



Directing my eye to an object 2 or 3 feet from me, I see it 

 distinctly enough whilst an object in the same field of view at the 

 distance of 1 or 1 2 feet is at the same moment seen very indistinctly. 

 If now, I direct my eye to the object at the distance of 10 or 12 feet, 

 I see it distinctly enough, but the object at the distance of 2 or 

 3 feet now appears very indistinct. 



This is commonly considered an evidence of adjustment of the eye 

 VOL. x. 2 E 



