PHILOSOPHICAL TRANSACTIONS 
OP THE 
ROYAL SOCIETY OP LONDON. 
Series A, Vol. 216. Pp. 91-128 
THE THRESHOLD OF VISION FOR DIFFERENT 
COLOURED LIGHTS. 
BY 
Sir W. de W. ABNEY, K.C.B., D.C.L., D.Sc., F.R.S., 
AND 
Prof. W. WATSON, D.Sc., F.R.S. 
LONDON: 
c 
PUBLISHED BY THE ROYAL SOCIETY, 
AND SOLD BY HARRISON AND SONS, ST. MARTIN’S LANE, W.C., 
Printers tn Orirtuarg to fHaje^tg. 
1915. 
A 540. 
Price Three Shillings. 
6.12.15 
