and Experiments on Vision . 391 
still no motion was to be seen. Dr. Young has made similar 
\ 
experiments with a similar event ; but he thinks that no argu- 
ment can hence be derived against his opinion, as neither can 
motion be excited in the uvea, by any artificial stimulus. In 
the first place, however, it is not agreeable to just reasoning 
to regard an unknown thing as an exception to a general rule, 
rather than as an example of it ; in the second, the motions 
of the uvea are involuntary, whereas the adaptation of the eye 
is, in part at least, under the command of the will ; and in 
the third, the crystalline seems very unfit for performing the 
motions which he assigns to it ; for if its figure be altered out 
of the body, by external force, it does not restore itself, but 
retains the shape which has been given to it, like a piece of 
dough, or soft clay. Possibly further experiments with Bel- 
ladonna may contribute to remove the obscurity, which at 
present surrounds this subject. 
