(°° 492) 
On Single and Correct Vision, by means of Double and Inverted 
Images on the Retine. By W. P. Autson, M.D. F.R.S.E. 
Professor of the Institutes of Medicine in the University of 
Edinburgh. 
(Read 11th April 1836.) 
In entering on a question which may be said to occupy a por- 
tion of the debateable land between Physiology and Metaphy- 
sics, it seems, in the first place, necessary to state with precision 
the nature of the difficulty, which has long been felt on this sub- 
ject, and endeavour to determine the degree to which it is rea- 
sonable to expect, that this difficulty may be removed ; and on 
these points there is such a discrepancy of opinion, even among 
the latest and most esteemed authors, as obviously to make far- 
ther inquiry desirable. 
No one can be more thoroughly convinced than I am, of the 
utter futility and absurdity of all attempts “ to shoot the gulf 
which separates the sensible world from the sentient soul.” In 
all our inquiries in the Physiology of the Nervous System, as 
connected with mental acts, we must keep in mind, that the end 
of these inquiries can only be, to determine the physical condi- 
tions under which the different mental phenomena take place ; 
and those under which, when they have taken place, they affect 
the different organs of the body. The question, how it comes 
about, that when those conditions are fulfilled, these results fol- 
low, must be held, in every case, to be beyond our powers. 
But as it is clearly in our power to ascertain the general condi- 
tions under which any mental phenomena are connected with a 
living body, so it may also be in our power to ascertain the special 
conditions under which any particular idea, or other mental act, 
takes place ; and particularly, to determine the exact sensations 
with which any particular notion formed in the mind is naturally 
