on Muscular Motion. 
7 
Making these experiments fatigued the eye considerably, 
and repeating them after very short intervals made the eye 
water, and gave a slight degree of pain ; this, however, soon 
went off. 
In looking at objects through this glass, the image was free 
from any tinge of colour, unless he directed his eye towards the 
circumference of the glass, and then it had a considerable 
tinge, which evidently arose from the prismatic figure of that 
part of the glass. 
A comparative experiment was made upon the perfect eye, 
with a glass of 15 inches focus. Objects were found in one ex- 
periment to appear most distinct at 8^- inches, the extremes 
3 inches and 1 1 inches ; in another, most distinct at 7 inches, 
the extremes as before, 3 and 1 1 inches. 
On the 29th of December, 34 days after the operation, the 
following experiments were made by candle-light, about six 
o'clock in the evening. 
The experiment with the double convex glass was repeated, 
the aperture being diminished to - 3 3 of an inch ; objects ap- 
peared most distinct at 5 inches, the extremes 3 inches and 
inches. The aperture was diminished to of an inch, and 
vision appeared most distinct at 5 inches, the extremes 31- 
inches and 7 inches. When the aperture was reduced to - 1 - of 
an inch, the inflexion of the rays produced the appearance of 
a speck, which obscured his vision. 
By diminishing the aperture, spherical aberration was in a 
great measure corrected, and vision rendered more distinct. 
A plano-convex glass of 2|- inches focus, with the plane 
towards the eye, was now applied, and the objects were most 
distinct at 6 inches, but by no means well defined : the aper- 
