16 The Theory of the Aether 



Cambridge by the intervening Plague " ; this was in 1666, and 

 his memoir on the subject was not presented to the Koyal 

 Society until five years later. In it he propounds a theory of 

 colour directly opposed to that of Hooke. " Colours," he says, 

 "are not Qualifications of light derived from Refractions, or 

 Reflections of natural Bodies (as 'tis generally believed), but 

 Original and connate properties, which in divers Rays are divers. 

 Some Rays are disposed to exhibit a red colour and no other : 

 some a yellow and no other, some a green and no other, and so 

 of the rest. Nor are there only Rays proper and particular to 

 the more eminent colours, but even to all their intermediate 

 gradations. 



" To the same degree of Refrangibility ever belongs the 

 same colour, and to the same colour ever belongs the same 

 degree of Refrangibility." 



" The species of colour, and degree of Refrangibility proper 

 to any particular sort of Rays, is not mutable by Refraction, nor 

 by Reflection from natural bodies, nor by, any other cause, that 

 I could yet observe. When any one sort of Rays hath been 

 well parted from those of other kinds, it hath afterwards 

 obstinately retained its colour, notwithstanding my utmost 

 endeavours to change it." 



The publication of the new theory gave rise to an acute 

 controversy. As might have been expected, Hooke was foremost 

 among the opponents, and led the attack with some degree of 

 asperity. When it is remembered that at this time Newton 

 was at the outset of his career, while Hooke was an older man, 

 with an established reputation, such harshness appears par- 

 ticularly ungenerous; and it is likely that the unpleasant 

 consequences which followed the announcement of his first 

 great discovery had much to do with the reluctance which 

 Newton ever afterwards showed to publish his results to the 

 world. 



In the course of the discussion Newton found occasion to 

 explain more fully the views which he entertained regarding 

 the nature of light. Hooke charged him with holding the 



