1892.] Capi. W. cle W. Ahneij on the Sensitiveness of the Eye, &c. 601 



WEEKLY EVENING MEETING, 



Friday, May 6, 1892. 



Sib Frederick Bramwell, Bart. D.C.L. F.R.S. Honorary Secretary 

 and Vice-President, in the Chair. 



Captain W. de W. Abney, C.B. R.E. D.C.L. F.R.S. 



The Sensitiveness of the Eye to Light and Colour. 



There may be some here who have had the pleasure — or the 

 pain — of rising very much betimes in a Swiss centre of moun- 

 taineering in order to gain some mountain peak before the sun has 

 had power enough to render the intervening snow- fields soft, or 

 perhaps dangerous. Those who have, will recollect what were the 

 sensations they experienced as they sallied out of the comfortable 

 hotel, after endeavouring to swallow down breakfast at 2 a.m., into 

 the darkness outside. Perhaps the night may have been moonless, 

 or the sky slightly overcast, and the sole light which greeted them 

 have been the nervous glimmer of the guides' lanterns. By this 

 feeble light they may have picked their way over the stony path, and 

 between the frequent stumbles over some half hidden piece of rock 

 lying in the short grass they may have had time to look around 

 and above them, and notice that the darkness of the night was alone 

 broken by stars which gave a twinkle through a gap in the clouds, 

 or if the sky were cloudless, every star would be seen to lie on a very 

 slightly illuminated sky of transparent blackness. Although giant 

 mountains may have been immediately in front of them, their out- 

 lines would be almost if not quite invisible. As time went on the 

 sky would become a little brighter, and what is termed the petit jour 

 would be known to be approaching. The outlines of the mountains 

 beyond would become fairly visible, the tufts of grass and the flowers 

 along the path would still be indistinguishable, and most things would 

 be of a cold grey, absolutely without colour. The guide's red woollen 

 scarf which he bound round his neck and mouth would be black 

 as coal. But a little more light, and then some flowers amongst the 

 grass would appear as a brighter grey, though the grass itself would 

 still appear dark ; but that red scarf would still be as black as a 

 funereal garment. The mountains would have no colour. The sky 

 would look leaden, and were it not for the stars above it might be a 

 matter of guesswork whether it were not covered over with cloud. 



More light still, and the sky would begin to blush in the part 

 where the sun was going to rise, and the rest would aj)pear as a blue- 

 grey ; the blue flowers will now be blue, and the white ones white ; 

 the violet or lavender coloured ones will still appear of no particular 

 colour, and the grass will look a green grey, whilst the guide's neck- 

 gear will appear a dull brown. 



Vol. XIII. (No. 86.) 2 s 



