1 64 SEVENTEENTH CENTURY. PT. in. 



CHAPTER XX. 



SCIENCE OF THE SEVENTEENTH CENTURY (CONTINUED). 



Newton's Discovery of the Dispersion of Light Traces the amount 

 of Refraction of each of the Coloured Rays Makes a Rotating 

 Disc turning the colours of the Spectrum into white Light 

 Reason why all Light passing through glass is not Coloured 

 Mr. Chester More Hall discovers the Difference of Dispersive Power 

 in Flint and Crown Glass Newton's Papers destroyed by his pet 

 dog Last years of Newton's life. 



Newton publishes Ms Discovery of the Dispersion of 

 Light, 1671. We must now return to Newton, and consider 

 his third great discovery, which was about light. You will 

 remember that he had to wait sixteen years between his first 

 attempt to investigate the law of gravitation, and that new 

 measurement of the earth which enabled him to prove the 

 truth of his theory. During this time he had by no means 

 been idle. He once said that the reason he had succeeded 

 in making discoveries was that he gave all his attention to 

 one subject at a time ; from 1666 to 1671, when his papers 

 on gravitation were quite laid aside, the subject to which he 

 devoted himself was Light. 



In the early part of the seventeenth century several 

 people had tried to find out what it was that gave rise to 

 different colours. An Italian archbishop named Antonio 

 de Dominis (died 1625) had given a better explanation of 

 the rainbow than Roger Bacon had given before him ; and 



