445 



the common opinion to be well founded, that the magnitude of the 

 pupil varies according to the distance of the object viewed. He 

 names, however, one extraordinary instance of a lady, whose pupil 

 contracts only when she views objects at the distance of nine inches, 

 but at other times is dilated very nearly to the full extent of the rim 

 of the cornea. 



Mr. Ware has also made experiments similar to those of Dr. Wells, 

 on the alteration of the power of the eye during that dilatation of 

 the pupil which is produced by the external application of belladonna. 

 Those of the author were attended with the same result of length- 

 ening the focus of either eye to which the belladonna was applied, 

 without affecting the customary range of vision in the other eye. 



The author observes, that short-sightedness does not depend on 

 the greater or less concavity of the cornea alone ; since its distance 

 from the retina, and the convexity of the crystalline also, must be 

 taken into the account. 



It has sometimes been observed, that old persons have in a short 

 time recovered the perfect sight of younger persons ; and this has 

 been explained by Dr. Porterfield, by a supposition of the absorption 

 of fat from the bottom of the orbit, allowing the axis of the eye to 

 become more elongated : but Mr. Ware thinks it more likely to have 

 arisen from absorption of the vitreous humour, in consequence of 

 which the sclerotica would be pressed inwards, and that then the 

 axis of the eye would be elongated. 



Mr. Ware observes, that persons in general who use glasses, pos- 

 sess the power of seeing both near and distant objects with the same 

 glass, but that this is not the case with those who have been couched, 

 who always require a different glass to enable them to see distant 

 objects ; proving thereby that the adapting power of the eye depends 

 on the presence of the crystalline. In consequence of this defect, 

 such persons judge very imperfectly of distances. 



In comparing the range of adaptation possessed by short-sighted 

 persons with that of others, the author conceives the range of the 

 former to be much less ; his estimate being made by the number of 

 inches through which the range of distinct vision extends. 



The author, being himself very short-sighted, remarks, that the 

 change that has taken place in his own eyes by age, does not accord 

 with the observation generally made, that short-sighted persons be- 

 come less so as they advance in life. In his eyes the shortest distance 

 of distinct vision remains nearly where it was ; but the power of dis- 

 cerning distant objects is so far lessened, that for this purpose he re- 

 quires a glass one degree deeper than that which he commonly em- 

 ploys, and with which he formerly used to distinguish distant as well 

 as near objects ; and as he is acquainted with other instances in which 

 a correspondent change has taken place, he is of opinion that such 

 changes are by no means unfrequent. However, in two of those here 

 enumerated, this change was produced by evident disease ; and in 

 one of them it was only temporary. A third instance mentioned of 

 an eye becoming less long-sighted, is occasioned by unusual efforts 



