382 



CHAPTER III. 



DISCOVERY OF THE LAW OF DISPERSION BY 

 REFRACTION. 



EARLY attempts were made to account for the 

 colours of the rainbow, and various other 

 phenomena in which colours are seen to arise from 

 transient and unsubstantial combinations of media. 

 Thus Aristotle explains the colours of the rainbow 

 by supposing 1 that it is light seen through a dark 

 medium : " Now," says he, " the bright seen through 

 the dark appears red, as, for instance, the fire of 

 green wood seen through the smoke, and the sun 

 through mist. Also 2 the weaker is the light, or 

 the visual power, and the nearer the colour ap- 

 proaches to the black; becoming first red, then 

 green, then purple. But 3 the vision is strongest in 

 the outer circle, because the periphery is greater; 

 thus we shall have a gradation from red, through 

 green, to purple, in passing from the outer to the 

 inner circle." This account would hardly have 

 deserved much notice, if it had not been for a 

 strange attempt to revive it, or something very like 

 it, in modern times. The same doctrine is found 

 in the work of De Dominis 4 . According to him, 

 light is white : but if we mix with the light some- 



1 Meteor, iii. 3. p. 373. 2 Ib. p. 374. * Ib. p. 375. 

 4 Cap. iii. p. 9. See also Gbthe Farbenl. vol. ii. p. 251. 



