S8 Mr, Ware's Observations on the near 



1811, has taken pains to ascertain, whether the power by 

 which the eye is adjusted to see at different distances, depends 

 in any degree on the faculty in the pupil of dilating and con- 

 tracting; and whether its fixed dilatation has any influence in 

 preventing an accurate view of near objects. This last men- 

 tioned effect Dr. Wells relates to have taken place remark- 

 ably in the case of Dr. Cutting, whose pupil being fixed 

 ki a dilated state by the action of the extract of belladonna, 

 perfect vision of a near object was removed, as the dilatation 

 advanced, from six inches (which was the nearest distance at 

 which Dr. Cutting could distinctly see the image of the flame 

 of a candle reflected from the bulb of a small thermometer,) 

 to seven inches in thirty minutes, and to three feet and a half 

 in three quarters of an hour. My eldest son, who has a very 

 extensive range of vision, has made a similar experiment on 

 his right eye with a similar result. Previous to the applica- 

 tion of the belladonna, he could bring the apparent hnes 

 on an optometer (Hke that improved by Dr. Young from 

 the invention of Dr. Porterfield, and described in the Phi- 

 losophical Transactions for the year 1800) to meet at four 

 inches from the eye ; and, by directing his attention to a more 

 distant point, he could prevent them from meeting till they 

 were seven inches from the eye, after which they continued 

 apparently united the whole length of the optometer, which 

 v/as twelve inches.* He could see the image of a candle 



• The two lines that are perceived on looking through the slits of an optometer, 

 cross each other precisely in the point from whence the rays of light diverge in 

 order to be brought to a focus on the retina. And their apparent union before and 

 after this point is occasioned by the unavoidable thickness of the line drawn on the 

 optometer. 



