Dr. Hosack's Observations on 'Vision. 203 
the layers themselves, in which these muscles are found, and 
which of course are larger, and more easily observed ; but, 
with his accuracy of observation, he has computed, that there 
are near 2000 laminas ; and according to Mr. Young, suppos- 
ing each layer to contain six muscles, we have necessarily, in 
all, 12,000 muscles ; the action of which certainly exceeds 
human comprehension. I hope this will not be deemed trifling 
minuteness, as it is a necessary and regular consequence, if 
we admit their existence as described. 
But secondly, as to the existence of these muscles, I 
cannot avoid expressing a doubt. With the utmost ac- 
curacy I was capable of, and with the assistance of the best 
glasses, to my disappointment, I cannot bear witness to the 
same circumstances related by Mr. Young, but found the 
lens perfectly transparent ; at the same time, lest it might be 
attributed to the want of habit in looking through glasses, I 
beg leave to observe, that I have been accustomed to the use 
of them in the examination of the more minute objects of 
natural history. After failing with the glasses in the natural 
viscid state of the lens, I had recourse to another expedient ; 
I exposed different lenses before the fire to a moderate degree 
of heat, by which they became opaque and dry ; in this state 
it is easy to separate the layers described by Mr. Young; but 
although not so numerous as noticed by the accurate Leeuwen- 
hoek, still they were too numerous to suppose each to have 
contained six muscles ; for I could have shewn distinctly at 
least fifty layers, without the assistance of a glass, as was 
readily granted by those to whom I exhibited them. 
But a circumstance which would seem to prove that these 
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