and Experiments on Vision. 385 
IV. Being now in possession of a new instrument, I next 
attempted to gain, by means of it, some illustration of the 
changes, which the vision of short-sighted persons undergoes 
from age. 
It has been very generally, if not universally, asserted by 
systematic writers upon vision, that the short-sighted are ren- 
dered by age fitter for seeing distant objects than they were 
in their youth. But this opinion appears to me unfounded in 
fact, and to rest altogether upon a false analogy. If those 
who 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 fol- 
lows, that the short-sighted must, from similar changes, be- 
come 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 young, and two have lately become, in respect to dis- 
tant objects, more short-sighted than they were formerly. As 
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 in early life, and as his profession obliged him to at- 
tend very much to minute visible objects, he for many years 
wore spectacles with concave glasses almost constantly, by 
the aid of which he saw as distinctly, and at as great a variety 
MDeccxr. 3 D 
