s 
Mr. Home's Lecture 
takes place ; one where the muscles of the eye do not corre- 
spond in their action, and therefore the two eyes do not bear 
equally upon the object ; the other, where some change has 
taken place in the refracting media of one eye which prevents 
the pencils of light from impressing the corresponding parts of 
the retina of both eyes. Instances of double vision produced 
by these two modes have fallen under my notice. 
It has been long ascertained by experiments, that when the 
•eyes are not turned equally towards an object, it appears 
double, and the disease in the muscles which produces this 
effect is the subject which I now mean to consider. It will, at 
the same time, be proper to distinguish this kind of double vi- 
sion from that which is produced by a change in the refracting 
media of the eye ; and this will be best done by explaining the 
nature of those changes in consequence of which it occurs. 
When one eye has had the crystalline lens extracted, the 
other remaining perfect, objects seen by both eyes will appear 
double. 
This is a fact which was noticed in a former lecture, in treat- 
ing of the adjustment of the eye. At first it appeared difficult 
to account for the double vision, particularly as the two images 
were entirely separate from each other. It could not arise from 
the absence of the lens, as that would not alter the situation of 
the images on the retina ; and the two images being of different 
dimensions on similar parts of the retina, would appear to be 
one before the other. As the operation of extracting the lens in 
no respect affects the muscles of the eye, the action of the mus- 
cles would be the same as before, and therefore could not con- 
tribute to produce this effect. 
The double vision in this instance appears to arise from the 
