Page:Proceedings of the Royal Society of London Vol 1.djvu/432

Rh but he found their power of adaptation too far diminished by age for such a trial. He however prevailed on Dr. Cutting, a young physician of his acquaintance, to make trial of it. The result was perfectly conformable-to the supposition. The dilatation of the pupil, it is true, commenced sooner than any other affection of the eye ; but in the course of three quarters of an hour, the eye, which before the experiment could see at six inches, could not now see at less than three feet and a half: and when its pupil had acquired the greatest dilatation, the rays from a. candle, even at eight feet distance, could not be made to converge on the retina, but only those from stars, or from very distant lamps. The defect thus occasioned by belladonna was found nearly in the same state on the following day; and it was not till the ninth day that the power of adapting the eye to near objects was completely restored. During the whole of this time it was observed that the affection was wholly conﬁned to the left eye, on which the experiment was made, and that the right eye remained unaltered; and in the same manner, when the experiment was after- wards repeated on the right, the left was then wholly unaffected by the belladonna.

The next observations relate to the changes which naturally take place in different eyes by age. With respect to those who are short- sighted, it has been generally asserted by systematic writers, and generally believed by others, that their eyes are rendered ﬁtter for seeing distant objects; but Dr. Wells has observed, in various in- stances, that this was not the case.

One gentleman, a fellow of this Society, who was short-sighted in early life, and consequently in the habit of using spectacles with concave glasses constantly, could see with them perfectly at a great variety of distances till he arrived at the age of ﬁfty. But he then began to observe that distant objects viewed through the glasses to which he had been accustomed, were indistinct; and he found it necessary to use others which were more concave for seeing objects at great distances. But along with this change of his sight, another occurred of an opposite kind : for he now found, that when he Wished to examine minute objects attentively, it was necessary to remove his spectacles entirely, and employ the naked eye alone. It was true, therefore, that, with respect to near objects, he had become longer- sighted, but in fact his range of vision was shortened equally at the opposite extreme, so that the mean is little altered from what it always has been.

In a second instance the variation produced by age in a short—sighted person was the same in kind, but not hitherto in so great degree.

In a few trials which Dr. Wells has made upon short-sighted persons with belladonna, the diminution of the range of adaptation has not taken place at both extremities, but the power of seeing near objects has alone been diminished.

He is not, however, altogether satisﬁed with these experiments; and designs to pursue them further, and at some future time to communicate the results to the Society.