48 
two distances of the luminous point from the front of the cornea 
(with sufficient accuracy) when these two appearances presented 
themselves; the card being made to slide upon a graduated 
scale whose end rested against the orbital bone of the eye, and 
the eye view being directed steadily forward. I may here men- 
tion that the method of experimenting in the subsequent obser- 
vations has been precisely the same. 
The second communication was dated 1846, January 14, or 
more than twenty-one years after the first. In this, besides giving 
the elements of astigmatism of the left eye, in the same manner 
in which I had given them in 1825, I gave the measure of the 
focal length of the right eye, which is perfectly stigmatic. 
After another period of more than twenty years, I am now 
enabled to give similar measures for both eyes. 
The comparison of the similar elements at the three different 
epochs may perhaps be interesting. 
I. Distance from the cornea of the left eye at which the 
luminous point presents the appearance of a nearly hori- 
zontal line. 
In 1825, 3:5 inches; Reciprocal = :286. 
Inv tSAG. 407° 28 oe OAL 
Ta: P866) 54 Priest. denigs, 9) einer 
Difference — ‘073. 
II. Distance from the cornea of the left eye at which the 
luminous point presents the appearance of a nearly 
vertical line. 
In 1825, 60 inches; Reciprocal *166. 
Tn S46. 3:9 i... |S sists 112. 
i 1sce t06) ee cook: UN 
Difference — ‘054. 
III. Measure of the astigmatic power of the left eye at dif- 
ferent epochs; estimated in each case by the differences 
of the reciprocals in the last table. 
