72 DISSERTATION SECOND. [mrtii. 



be made out both by analysis and composition. The white 

 light of the Sun can be separated, as we have just seen, 

 into the seven simple colours ; and if these colours be united 

 again thev form white. Should any of them have been 

 wanting, or not in its due proportion, the white produced is 

 defective. 



It appeared, too, that natural bodies, of whatever colour, 

 if viewed by simple and homogeneous light, are seen of the 

 colour o£that light and of no other. Newton tried this very 

 satisfactory experiment on bodies of all colours, and found it 

 to hold uniformly ; the light was never changed by the colour 

 of the body that reflected it. 



Newton, thus furnished with so many new and accurate 

 notions concerning the nature and production of colour, pro- 

 ceeded to apply them to the explanation of phenomena. 

 The subject which naturally offered itself the first to this analy- 

 sis was the rainbow, which, by the grandeur and simplicity 

 o{ its figure, added to the brilliancy of its colours, in every 

 age has equally attracted the attention of the peasant and of 

 the philosopher. That two refractions and one reflection 

 were at least a part of the machinery which nature employed 

 in the construction of this splendid arch, had been known 

 from the time of Antonio de Dominis -, 1 and the manner in 

 which the arched figure is produced had been shown by 

 Descartes ; so that it only remained to explain the nature of 

 the colour and its distribution. As the colours were the same 

 with those exhibited by the prism, and succeeded in the same 

 order, it could hardly be doubted that the cause was the 

 same. Newton showed the truth of his principles by calcu- 

 lating the extent of the arch, the breadth of the colour- 

 ed bow, the position of the secondary bow, its distance 

 from the primary, and by explaining the inversion of the 



1 Note F, at the end. 



