MEMOIR VII.J STUDIES IN THE DIFFRACTION SPECTRUM. 129 



that light is a pure un decomposable elementary principle. 

 He showed that this conclusion must be modified. No 

 one, except Leibnitz, in those days, and no one for a long 

 time subsequently, discerned the ominous import of the 

 discoveries of this Prince of geometers. Of his detec- 

 tion of the origin of Kepler's laws, and its necessary 

 consequence of the mode in which the government of 

 the universe is conducted, I have nothing here to say. 

 Let us see how it was with his discoveries concerning 

 light. 



His interpretation of the experiment he made in the 

 "dark chamber" was this, that light is not an undecom- 

 posable element, as was at that time supposed, but that 

 in reality it consists of not fewer than seven different 

 constituents, recognizable by their color. These, if mixed 

 in any manner together, whether by grinding tinted pig- 

 ments or revolving parti colored sectors, or converging 

 the spectrum through a convex lens, would, by their 

 union, produce white light. His felicitous experiment 

 with the two reversed prisms silenced the carping critics 

 of that day, who had declared that the colored tints 

 with which he was working had no such origin as he 

 affirmed in difference of refrangibility but were anal- 

 ogous to the iridescent play of light on a pigeon's breast, 

 or the more gorgeous lustre of a peacock's tail. It cost 

 only a short struggle, and the theory of the composite 

 nature of light made good its ground. 



When, therefore, Herschel, in his examination of the 

 sun's surface through colored glasses, came to the conclu- 

 sion that the heat emitted by the sun is essentially and 

 intrinsically distinct from the light, and that these ele- 

 ments may be parted from each other by refraction, he 

 did no more than develop the principle that had been 

 announced by Newton ; and when, at a later period, 

 Melloni extended these researches, and it was universal- 



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