aftd distant Sight of different Persons. 33 



colleges, they are used by a considerable proportion of the 

 whole number in both Universities ; and, in one college in 

 Oxford, I have a list of the names of not less than thirty-two out 

 of one hundred and twenty-seven, who wore either a hand glass 

 or spectacles, between the years 1803 ^^^^ 1807. It is not impro- 

 bable, that some of these were induced to do it solely because 

 the practice was fashionable; but, I believe, the number of such 

 is inconsiderable, when compared with that of those whose 

 sight received some small assistance from them, though this 

 assistance could have been dispensed with, without inconve- 

 nience, if the practice had not been introduced. The misfor- 

 tune resulting from the use of concave glasses is this, that the 

 near sightedness is not only fixed by it, but a habit of inquiry 

 is induced with regard to the extreme perfection of vision ; 

 and, in consequence of this, frequent changes are made for 

 glasses that are more and more concave, until at length the near 

 sightedness becomes so considerable, as to be rendered seri- 

 ously inconvenient and afflicting. It should be remembered, 

 that, for common purposes, every near sighted eye can see 

 with nearly equal accuracy through two glasses, one of which 

 is one number deeper than the other ; and though the sight 

 be in a slight degree more assisted by the deepest of these 

 than by the other, yet on its being first used, the deepest 

 number always occasions an uneasy sensation, as if the eye 

 was strained. If, therefore, the glass that is most concave be 

 at first employed, the eye, in a little time, will be accommo- 

 dated to it, and then a glass one number deeper may be used 

 with similar advantage to the sight; and if the wish for en- 

 joying the most perfect vision be indulged, this glass may 

 soon be changed for one that is a number still deeper, and so 



MDCCCXIII. F 



