474 Dr Auison on Single and Correct Vision, by means of 
ject touched by us, had produced, not two merely, but two thou- 
sand separate images in our eyes, erect or inverted, or in any in- 
termediate degree of inclination, the visual feeling thus excited 
would still have accompanied the touch of a single object ; and if 
only it had accompanied it uniformly, the single object. would 
have been suggested by it, precisely in the same manner as it is 
now suggested by the particular visual feeling that attends the 
double inverted image.” * 
But, with all deference to this illustrious metaphysician, I will 
take the liberty of stating, that this view of the subject had been 
previously fully considered, and, as far as I can judge, completely 
set aside by Dr Rein, at least in reference to single vision by 
two images on the retinz ; and that, not by any abstract reason- 
ing, but by appeal to facts. 
If it were only by experience, and association with the per- 
ceptions of touch, that we learned that any object placed before 
the eyes, and seen by two images, is nevertheless single, it seems 
prima facie reasonable to conclude, that we should never see an 
object double, which we know by touch to be single; whereas 
we all know, that if, by pressure on the ball of one eye, or by 
any other means, we direct the axes of the two eyes to different 
points in an object, we immediately see it double, and cannot, by 
any means, avoid seeing it double, so long as that condition of 
the eyes continues, notwithstanding the full conviction, derived 
from touch, of its being single. 
The only answer that I can conceive to this is, that the asso- 
ciation, by which we are informed of an object of sight being 
single, is formed with the natural and healthy state of the vision 
of that object, when the axes of the two eyes are directed to the 
same point in the object, and its images are formed on corre- 
sponding points of the retinz of the two eyes; and that when 
its images are formed on dissimilar points of the retinz, the diffe- 
* Lect. 29. 
