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', 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 



5 Gothe, p. 263. * Meteor. Sect. viii. p. 190. 



7 Sect. vii. p. 192. 



