LAW OF DISPERSION BY REFRACTION. 383 



thing dark, the colours arise, first red, then green, 

 then blue or violet. He applies this to explain the 

 colours of the rainbow 5 , by means of the consi- 

 deration that, of the rays which come to the eye 

 from the globes of water, some go through a larger 

 thickness of the globe than others, whence he ob- 

 tains the gradation of colours just described. 



Descartes came far nearer the true philosophy 

 of the iridal colours. He found that a similar 

 series of colours was produced by refraction of light 

 bounded by shade, through a prism 6 ; and he rightly 

 inferred that neither the curvature of the surface 

 of the drops of water, nor the reflection, nor the 

 repetition of refraction, were necessary to the gene- 

 ration of such colours. In further examining the 

 course of the rays, he approaches very near to the 

 true conception of the case ; and we are led to 

 believe that he might have anticipated Newton in 

 his discovery of the unequal refrangibility of dif- 

 ferent colours, if it had been possible for him to 

 reason any otherwise than in the terms and notions 

 of his preconceived hypotheses. The conclusion 

 which he draws is 7 , that "the particles of the subtile 

 matter which transmit the action of light, endeavour 

 to rotate with so great a force and impetus, that 

 they cannot move in a straight line (whence comes 

 refraction) : and that those particles which endea- 

 vour to revolve much more strongly produce a red 



8 Gothe, p. 263. ' Meteor. Sect. via. p. 190. 



' Sect. vii. p. 192. 



