656 
Proceedings of the Royal Society 
paper rendered translucent by oil, &c. In showing the experiment 
to others, I have found that certain people do not see the resultant 
colour, whilst others do so readily. The cause of this and of the 
opposite statements of the observers above alluded to, I believe to 
be this : The sensation resulting from the fusion in the brain of the 
two impressions, one coming from each eye, appears to be capable 
of decomposition by a mental effort. Thus, the purple produced 
by red and blue appears as such to my eye so long as I simply look 
at it without any conscious effort ; but if I wish to analyse it, I 
then find that the two colours, red and blue, seem to be superposed 
on each other, and the one appears to shine through the other. On 
ceasing to make any effort, they again fuse together as before. 
Again, by thinking of the colour opposite the right eye, say red, the 
field ceases to be purple and has a decided tinge of red, and on 
thinking of the colour before the left eye, say blue, the prevailing 
tone of the field is blue. Apparently, then, if corresponding points 
of two retinae be simultaneously stimulated by two different colours, 
the impressions are fused in consciousness into the resultant colour ; 
but the resulting sensation may be decomposed by an act of atten- 
tion. The decomposition is effected partly by strongly directing 
the attention to one eye, and less strongly to the other, and the 
result is a sensation corresponding to the colour placed before the 
eye to which the attention is most strongly directed. Some of the 
same facts may be studied with the aid of the stereoscope. 
The following Gentlemen were duly elected Fellows of the 
Society : — 
Alex. Macfarlane, M.A. , B.Sc., 2 Roseneath Terrace. 
Samuel Drew, M.D., D.Sc., Chapelton, near Sheffield. 
George M ‘Go wan, 24 Argyll Place. 
James Brunlees, Yice-Pres., Inst. C. E., 5 Victoria Street, Westminster. 
John Grahame Dalziel, 95 South Street, St Andrews. 
