OBSERVATIONS AND EXPERIMENTS ON VISION. 327 



they were in their youth. But this opinion appears to me 

 unfounded in fact, and to rest altogether upon a false 

 analogy. If those M^ho possess ordinary vision, when 

 young, become from the flatness of the cornea, or other 

 changes in the mere structure of the eye, long-sighted as 

 they approach to old age, it follows, that the short-sighted 

 must, from similar changes, become better fitted to see 

 distant objects. Such appears to have been their reasoning. 

 But the course pursued by nature seems very different from 

 that which they have assigned to her. For of four short- 

 sighted persons of my acquaintance, the ages of whom are 

 between fifty-four and sixty years, and into the state of 

 whose vision I have inquired particularly, two have not 

 observed that their vision has changed since they were 



Youne, and two have lately become, in respect to distant Short sight for 

 , • , , , L r I A distant objocts 



objects, more short-sighted than they were formerly. ASin^-fg^jgd 



the manner, in which this change has occurred, is unnoticed, 

 I believe, by any preceding author, I shall here relate the 

 more remarkable of the two cases. 



A gentleman, who is a fellow of this society, became Short-sighted 

 . , ,.„ , , . /. • 1.1- 1 1 • persons become 



short-sighted in early life; and as his profession obliged Jnmjnojggo ^^ 



to attend very much to minute visible objects, he for many remote objects, 

 years wore spectacles with concave glasses almost constant- 

 ly, by the aid of which he saw as distinctly, and at as 

 great a variety of distances, as those who enjoy the most 

 perfect vision. At the age of fifty, however, he began to 

 observe, that distant objects, though viewed through his 

 glasses, appeared indistinct, and he was hence led to fear, 

 that his eyes were affected with some disease. But happen- 

 ing one day to take up, in an optician's shop, a. single 

 concave glass, and to hold it before one of his eyes, while 

 his spectacles were on, he found to his great joy, that he 

 had regained distinct vision of distant objects. With regard 

 to such objects, therefore, he had lately become shorter 

 sighted than he had formerly been. But along with this 

 change, another occurred of a directly opposite kind. For^^^'J" ^'>' ""^^ 

 ■when he wished to examine a minute object attentively, such 

 as he used to see accurately by means of his spectacles, he 

 now found it necessary to lay them aside, and to employ 

 bis naked eye. He had become, therefore, in respect to 



near 



