ON THE PERCEPTION OF COLOUR. By Sir George 

 Gabriel Stokes, Bart., M.A., D.C.L., LL.D., F.R.S., The 



President. 



ON a former occasion I expressed the opinion that in further- 

 ance of the objects of the Victoria Institute, it would 

 be a useful thing from time to time to take stock, as it \vere, 

 of what is known in particular branches of science ; with the 

 view of assisting the general public in discriminating between 

 well-established scientific theories and hypotheses still on 

 their trial, or it may be mere conjectures, going far ahead of 

 actual evidence. At the Annual Meeting in 1895 I introduced 

 the subject of the luminiferous ether, a medium so mysterious 

 in its nature, and yet one through the intervention of Avhich 

 some effects are brouglit about which have received a 

 thoroughly satisfactory explanation. In the following year 

 I brouglit forward the subject of the perception of light, a 

 subject about which we know far less than about the nature 

 and laws of light objectively considered; I mean than 

 about such subjects as interference, diffraction, polarisation, 

 &c., in the study of which the eye is used merely as an 

 instrument of research, and may in certain cases be replaced 

 by a photographic plate or some other appliance. Even 

 when the subject was limited to the perception of light it 

 was still much too extensive to be gone into in the Annual 

 Address, and the branch I propose to notice to-day was 

 dismissed in very few words. I said (page 20),* " AVe do not 

 see light merely as light, but we see a great variety of 

 colour. We can distinguish one light from another light by 

 its colour, and not by its intensity only. It would take me 

 a great deal too long to give you any idea of what is known 

 ^ which after all is not much) as to the way in Avhich that is 

 effected." 



To bring such a subject before the Institute seems ill to 

 accord with the proposal I mentioned to " take stock " of 

 what is known in some particular department. Still, little 



* Transactions, vol. xxix. 



