LIGHT AND COLOURS. [LeSSOH XXV. 



Amongst them we must not pass by ihe phae- 

 nomenon of the variety of Colours t which are ob- 

 servable all over the face of nature, seeming pe- 

 culiarly adapted to increase the pleasure of man- 

 kind. Colours are nothing else than different sen- 

 sations excited in us by the variously refracted rays 

 of light being carried to our eyes in a different 

 manner, according to the different size, or shape, 

 or situation of the particles of which the surfaces 

 of bodies are composed. Colours, then, are not 

 inherent in the bodies which appear to wear them; 

 but they seem to arise from a capability or dispo- 

 sition in those bodies to reflect back particular 

 rays, and these rays possessing different degrees of 

 refrangibility produce the effect : thus it is found 

 that the least refrangible rays produce the idea of 

 a red Colour j and as the refrangibility increases, 

 the ideas of the intermediate Colours are excited, 

 till at length we arrive at the opposite extreme of 

 refrangibility, and then the sensation of a violet 

 Colour is produced. The primary Colours are, 

 according to NEWTON, seven in number, of these 

 I here present you with a poetical account: 



First the flaming red 



Sprung vivid forth ; the tawny orange next ; 



And next delicious yellow; by whose side 



Fell the kind beams of all-refreshing green; 



Then the pure blue, that swells autumnal skies. 



Etherial play'd; and then, of sadder hue, 



Emerg'd the deepen'd indico, as when 



The heavy-skirted evening droops with frost;. 



While the last gleanings of refracted Light 



Dj'd in the fainting violet away. THOMSON. 



Thus 



