on Muscular Motion. 
9 
The perfect eye, with a glass of 6 \ inches focus, had dis- 
tinct vision at 3 inches ; the near limit was i|- inch, the distant 
one less than 7 inches. 
The imperfect eye, with a glass inches focus, with an 
aperture of an inch, had distinct vision at 2|- inches, the near 
limit i|- inch, the distant one 7 inches. 
From the result of this experiment we find that the range 
of adjustment of the imperfect eye, when the two eyes were 
made to see at nearly the same focal distance, exceeded that 
of the perfect eye. 
These experiments were made by Mr. Ramsden, who took 
particular care to avoid every thing that might be productive 
of error or deception ; and repeated them several times before 
any conclusions were drawn from them. Several others were 
made on the same subject, but as they only tended to confirm 
those already mentioned, it would be taking up the time of 
this learned Society unnecessarily to detail them. 
It may be proper to mention a reason which suggested it- 
self to Mr. Ramsden, why the point of distinct vision of the 
imperfect eye appeared to the man himself nearer than it was 
in reality ; it arose from his judging of distinctness by the 
legibility of the letters, which were easier read when they sub- 
tended a greater angle (from the imperfection of his eye) than 
at his real point of distinct vision. 
The result of these experiments convinced us that the in- 
ternal power of the eye, by which it is adjusted to see at dif- 
ferent distances, does not reside in the crystalline lens ; we 
were also satisfied by the facts and arguments adduced in Mr. 
Hunter's letter on this subject, published in the first part 
of the last volume of the Philosophical Transactions, that it 
C 
MDCCXCV. 
