XVI. Observations on Vision. By Thomas Young. Communi- 
cated by Richard Brocklesby, M.D. F. R. S. 
Read May 30, 1793. 
It is well known that the eye, when not acted upon by any 
exertion of the mind, conveys a distinct impression of those 
objects only which are situated at a certain distance from it- 
self ; that this distance is different in different persons, and 
that the eye can, by the volition of the mind, be accommo- 
date’! to view other objects at a much less distance : but how 
this accommodation is effected, has long been a matter of 
dispute, and has not yet been satisfactorily explained. It is 
equally true, though not commonly observed, that no exer- 
tion of the mind can accommodate the eye to view objects at 
a distance greater than that of indolent vision, as may easily 
be experienced by any person to whom this distance of indo- 
lent vision is less than infinite. 
The principal parts of the eye, and of its appertenances, 
have been described by various authors. Winslow is ge- 
nerally very accurate ; but Albinus, in Musschenbroek j s 
In ro-‘u tii, has represented several particulars more correctly. 
I shall suppose their account complete, except where I men- 
tion or delineate the contrary. 
The first theory that I find of the accommodation of the 
