60 ADDRESS TO THE BRITISH ASSOCIATION, 1881. 



an end to the pretension of yellow to be considered a 

 primary element of color. From these and other 

 considerations it would seem, therefore, that the three 

 primary colors if such an expression be retained 

 are red, green, and violet. 



The existence of rays beyond the violet, though 

 almost invisible to our eyes, had long been demonstrated 

 by their chemical action. Stokes, however, showed in 

 1852 that their existence might be proved in another 

 manner, for that there are certain substances which, 

 when excited by them, emit light visible to our eyes. 

 To this phenomenon he gave the name of fluorescence. 

 At the other end of the spectrum Abney has recently 

 succeeded in photographing a large number of lines in 

 the infra-red portion, the existence of which was first 

 proved by Sir William Herschel. 



From the rarity, and in many cases the entire 

 absence, of reference to blue, in ancient literature, 

 Geiger adopting and extending a suggestion first 

 thrown out by Mr. Gladstone has maintained that, 

 even as recently as the tune of Homer, our ancestors 

 were blue-blind. Though for my part I am unable to 

 adopt this view, it is certainly very remarkable that 

 neither the Rigveda, which consists almost entirely of 

 hymns to heaven, nor the Zendavesta, the Bible of the 

 Parsees or fire-worshippers, nor the earlier books of the 

 Old Testament, nor the Homeric poems, ever allude to 

 the sky as blue. 



On the other hand, from the dawn of poetry, the 

 splendours of the morning and evening skies have ex- 

 cited the admiration of mankind. As Ruskin says, in 

 language almost as brilliant as the sky itself, the whole 



