IN OPTICS. 97 



maybe made evident by another experiment: 

 Place a convex lens in such a manner before 

 one eye, that the flame of a candle, at the 

 distance of two or three feet from the face, 

 may appear indistinctly terminated to that eye, 

 when both axes are pointed to it. The same 

 eye being kept fixed, let the two axes after- 

 ward meet beyond the flame, and it will now 

 be seen much better defined, though the pupil 

 is at the same time become larger. The insuf- 

 ficiency of the explanation of Aguilonius, is also 

 proved, by a circumstance frequently noticed 

 in persons who are very short-sighted ; for such 

 are observed, when they desire to view an ob- 

 ject with much attention, to hold it close to 

 one eye, and to turn the other aside ; in this 

 way occasioning the two axes to meet very re- 

 motely from the object. 



2. The reason commonly given, why short- 

 sighted people view an object with one eye 

 only in the manner above-mentioned, is, that 

 by this means they avoid the uneasy straining 

 of the muscles, which must be employed to 

 direct both axes to the same point. But it is 

 evident they must derive from the practice this 

 farther advantage, that, as their optic axes are 

 now parallel to each other, or nearly so, they, 

 consequently, see the object in the least refrac- 

 tive state of their eyes. Pencils, therefore, will 



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