An Appendix to Mr. Ware's Paper on Vision. 343 
Secondly ; though the usual effect of time on perfect eyes 
be that of inducing a necessity to make use of concave 
glasses, in order to see near objects distinctly, yet some- 
times even after the age of fifty, and after convex glasses 
have been used many years for this purpose, the eyes have 
not only ceased to derive benefit from them, when looking 
at near objects, but they have required concave classes to 
enable them to distinguish with precision objects at a di- 
stance. : 
’ Thirdly; though the cause of this change be not always 
known, yet sometimes it has been induced by the use of 
evacuating remedies, particularly of ieeches applied to the 
temples; and sometimes by looking through a microscope, 
for a continued length of time, in several successive days. 
Fourthly ; instances are not uncommon, in which per- 
sons far advanced in life, (viz. between eighty aud ninety,) 
whose eyes have been accustomed for a long time to the use 
of deeply convex glasses, when they have read or written, 
have ceased to derive benefit from these glasses, and they 
have become able, without any assistance, to see both near 
and distant objects almost as well as when they were young. 
Although it be not easy to ascertain the cause of this 
amended vision, it seems not improbable that it 1s occa- 
sioned by an absorption of part of the vitreous humour 5 
in consequence of which the sides of the eye collapse, and 
its axis from the cornea to the retina is lengthened, by 
which alteration the length of this axis is brought into the 
same proportion to the flattened state of the cornea or cry- 
stalline, or both, which it had to these parts before the 
alteration took place. ; 
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LVI. An Appendix to Mr. Warx’s Paper on Visions 
By Sir Cuares BLAGDEN, Pho. 
Maz. Wane states in his paper, that near-sightedness comes 
on most frequently at an early age; that it is more common 
in the higher than in the lower ranks of life ; and that par- 
ticularly at the universities, and various colleges, a large 
proportion of the students make use of concave glasses. 
‘All this is exactly true, and to be accounted for by one sin- 
le circumstance; namely, the habit of looking at near ob- 
jects. Children born with eyes which are capable of ad- 
orting- shepedys? to the most distant objects, gradually 
ose that power soon after they begin to read and write 5 
* From the Philosophical Transactions for 1813, part i, 
Y4 those 
