Dr. Hosack's Observations on Vision. 215 
observes, of the sight becoming gradually better for several 
months after the operation. 
When we have been long out of the habit of combining our 
muscles in almost any one action of life, as walking, dan- 
cing, or playing upon a musical instrument, we in a great 
measure lose the combination, and find a difficulty in recover- 
ing it, in proportion to the length of time we had been de- 
prived of it; but the individual action of each muscle remains 
as before. Thus, probably, with the muscles of the eye. A 
variety of facts of a similar nature must present themselves to 
every person conversant in the science of optics, which may 
admit of a similar explanation. 
I have thus endeavoured, first, to point out the limited action 
of the iris, and of consequence the insufficiency of this action 
for explaining vision. Secondly, to prove that the lens 
possesses no power of changing its form to the different dis- 
tances of objects. Thirdly, that to see objects at different 
distances, corresponding changes of distance should be pro- 
duced between the retina and the anterior part of the eye, as 
also in the refracting powers of the media through which the 
rays of light are to pass. And, fourthly, that the combined 
action of the external muscles is not only capable of produ- 
cing these effects, but that from their situation and structure 
they are also peculiarly adapted to produce them. 
Is it not then consistent with every principle in the oeconoray 
of nature and of philosophy, seeing the imperfections of the 
principles which have hitherto been employed in explaining 
the phenomena in question, to adopt the one before us, until 
(agreeable to one of the established rules in philosophizing) 
