/}36 HISTORY OF 



There are many reasons to induce us to think that such as 

 are near-sighted see objects larger than other persons; and yet 

 the contrary is most certainly true, tor they see them less. Mr 

 Buffon informs us that he himself is short-sighted, and that his 

 left eye is stronger than his right. He has very frequently ex- 

 perienced, upon looking at any object, such as the letters of a 

 book, that they appear less to the weakest eye ; and that when 

 he places the book, so as that the letters appear double, the 

 linages of the left eye, which is strongest, are greater than those 

 of the right, which is the most feeble. He has examined severa' 

 others, who were in similar circumstances, and has always found 

 that the best eye saw every object the largest. This he ascribes 

 to habit ; for near-sighted people being accu&tomed to come 

 close to the object, and view but a small part of it at a tune, the 

 habit ensues, when the whole of an object is seen, and it appears 

 less to them than to others. 



Infants having their eyes less than those of adults, must see 

 objects also smaller in pioportion. For the image formed on 

 the back of the eye will be lai'ge, as the eye is capacious ; and 

 infants having it not so great, cannot have so large a picture of 

 the object. This may be a reason also why they are unable to 

 see so distinctly, or at such distances, as persons arrived at ma- 

 turity. 



Old men, on the contrary, see bodies close to them very in- 

 distinctly, but bodies at a great distance from them with more 

 precision ; and this may happen from an alteration in the coats, 

 or perhaps, bumom's of the eye ; and not, as is supposed, from 

 their diminution. The cornea, for instance, may become too 

 rigid to adapt itself, and take a proper convexity for seeing mi- 

 nute objects J and its very flatness will be sufficient to fit it for 

 distant vision. 



When we cast our eyes upon an object extrem.ely brilliant, or 

 when we fix and detain them too long upon the same object, the or. 

 gan is hurt and fatigued, its vision becomes indistinc^t, and the image 

 of the body which has thus too violently or perseveringly employed 

 us, is painted upon eveiy thing we look at, and mixes with every 

 object that occurs. " And this is an obvious consequence of 

 the eye taking in too much light, either immediately, or by reflec- 

 tion. Every body exjiosed to the light, for a time, drinks in a 

 quantity of its rays, which being brought into darkness, it caimot 



