ANIMALS. i 1 9 



on which the colours are more faintly spread, and that, in some mea 

 sure, take a part of their hue from the air between us and them. 

 Bright objects, also, are seen at a greater distance than such as are 

 obscure; and, most probably, for this reason, that being less similar in 

 colour to the air which interposes, their impressions are less effaced 

 by it, and they continue more distinctly visible. Thus, a black and 

 distant object is not seen so far off as a bright and glittering .one. and 

 a fire by night is seen much farther off than by day." 



The power of seeing objects at a distance is very rarely equa* m 

 both eyes. When this inequality is in any great degree, the person 

 so circumstanced then makes use only of one eye, shutting that which 

 sees the least, and employing the other with all its power. And hence 

 proceeds that awkward look which is known by the name of strabism 



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

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

 trary is most certainly true, for they see them less. Mr. Buffon in- 

 forms us that he himself is short-sighted, and that his left eye is 

 stronger than his right. He has very frequently experienced, 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 images of the left eye, which is strongest, 

 are greater than those of the right, which is the most feeble. He has 

 examined several 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 accustomed to come 

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

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

 them than to others. 



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

 also smaller in proportion. For the image formed on the back of the 

 eye will be large, as the eye is capacious ; and infants, having it not 

 so great, cannot have so large a picture of the object. This may b 

 a reason also why they are unable to see so distinctly, or at such dis- 

 tances as persons arrived at maturity. 



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

 ly, but bodies at a great distance from them with more precision ; and 

 this may happen from an alteration in the coats, or, perhaps, humours 

 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 minute objects ; and its very flatness will 

 be sufficient to fit it for distant vision. 



When we cast our eyes upon an object extremely brilliant, or 

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

 is hurt and fatigued, its vision becomes indistinct, and the image oi 

 the body, which has thus too violently, or too perseveringly employed us, 

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

 that occurs. "And this is an obvious consequence of the eye taking 

 in too much ight, either immediately, or by reflection. Every body 

 exposed to the light, for a time, drinks in a quantity of its rays, whichj 

 being brought into darkness, it cannot instantly discharge. Thus th 

 hand, if it be exposed to broad day-light for some time, and then /> 



