355 
of Edinburgh, Session 1870-71. 
After all that has been read of the complete absence of any kind 
of Art amonst the savages of these islands and the neighbouring 
Andamans, one is irresistibly led to think that these objects are 
not the works of the natives, but have been produced by some 
debased European or other captive. 
2. Certain Phenomena applied in Solution of Difficulties con- 
nected with the Theory of Vision. By R. S. Wyld, Esq. 
The theory of vision has been the subject of much more scientific 
study than that of any of our other senses, but notwithstanding 
this, the subject is still encumbered with some difficulties and con- 
tradictions, the solution of which is essential to our having a true 
and complete theory. Such are the questions, — first, — regarding 
single and double vision, as depending on the excitement of cor- 
responding, or, as they are generally called, identical points of 
the retinse ; second, — the question whether perception is in the 
retinae or in the brain; and lastly, the question regarding the' 
decussation and ultimate course of the fibres of the optic nerves. 
Regarding the subject of single vision with two eyes, there has fre- 
quently been exhibited a great amount of misunderstanding ; since 
the discovery of the stereoscope, however, the nature of what has 
commonly, though not with strict propriety, been called single 
vision, has become much better understood. The truth is, there 
is no such thing as single vision when two eyes are in use, and 
a very little attention will make it clear how the case stands. 
Take two shillings of like appearance, and place them correctly 
and with the same sides up, in the different compartments of the 
stereoscope, but so far apart that they do not appear to coalesce. 
In this position they are distinctly seen by each eye as two 
separate objects. Cause the coins next gradually to approach till 
they seem to coalesce or unite into one — we say seem, for there is 
no true visual union. Even when they seem to unite, there are 
still two impressions made — one on each retina — and a correspond- 
ing impulse is from each of these membranes sent to the brain and 
to the mind, though from the close resemblance of the two im- 
pressions it may be impossible to distinguish the one from the 
other. 
