50 MEMORANDA. 
so that light can be transmitted from the mirror. Altoge- 
ther it is the best and most useful instrument we have seen. 
It is made by Mr. Charles Collins, 77, Great Titchfield 
Street, Oxford Street, from the plan of Dr. Lawson, Pro- 
fessor of Histology at St. Mary’s Hospital—Lancet. 
Note on Binocular Vision.—I have made what I consider a 
very important observation, and one which, so far as my 
reading is concerned (which is rather extensive on subjects of 
this kind), is new. I scarcely dare call it a discovery. 
In order to explain myself, I will relate a few observations 
which I made about thirteen years ago, when stereoscopic 
science was in its infancy. I must premise that for many 
years past it has been an uncontrollable habit of mine to 
converge the optic axes of my eyes upon any two objects of 
whatever kind, similar or dissimilar. The following experi- 
ments, made, as I said, thirteen years ago, astonished me 
amazingly. 
I laid myself on my back, with my head directly under a 
cane-bottomed chair, looking towards the ceiling of the room. 
I combined the two contiguous openings, when a beautiful 
example of solidity and lustre was produced; but when I 
combined one opening with the second from it, thus, 
the bottom of the chair instantly separated into 
662d two distinct planes, the one the natural distance, 
which I could touch with my finger, and the other removed 
to a considerable distance. But the strangeness of the thing 
consists in this, that the holes of the more distant ones were 
apparently double the size of the nearer ones, and the whole 
