LAW OF DISPERSION BY REFRACTION. Cl 



teaching distinctly that the law of refraction was to be applied, not tc 

 the beam of light in general, but to the colors in particular. 



When Newton produced a bright spot on the wall of his chamber, 

 by admitting the sun's light through a small hole in his window-shut- 

 ter, and making it pass through a prism, he expected the image to be 

 round ; which, of course, it would have been, if the colors had been 

 produced by an equal dispersion in all directions ; but to his surprise 

 he saw the image, or spectrum, five times as long as it was broad 

 lie found that no consideration of the different thickness of the glass, 

 the possible unevenness of its surface, or the different angles of rays 

 proceeding from the two sides of the sun, could be the cause of this 

 shape. He found, also, that the rays did not go from the prism to the 

 imao-e in curves : he was then convinced that the different colors were 



O 



refracted separately, and at different angles ; and he confirmed this opi- 

 nion by transmitting and refracting the rays of each color separately. 



The experiments are so easy and common, and Newton's interpreta- 

 tion of them so simple and evident, that we might have expected it to 

 receive general assent ; indeed, as we have shown, Descartes had 

 already been led very near the same point. In fact, Newton's opinions 

 were not long in obtaining general acceptance; but they met with 

 enough of cavil and misapprehension to annoy extremely the disco- 

 verer, whose clear views and quiet temper made him impatient alike 

 of stupidity and of contentiousness. 



"\Ve need not dwell long on the early objections which were made 

 to Newton's doctrine. A Jesuit, of the name of Ignatius Pardies, pro- 

 fessor at Clerniont, at first attempted to account for the elongation of 

 the image by the difference of the angles made by the rays from the 

 two edges of the sun, which would produce a difference in the amount 

 of refraction of the two borders ; but when Newton pointed out the 

 calculations which showed the insufficiency of this explanation, he 

 withdrew his opposition. Another more pertinacious opponent 

 appeared in Francis Linus, a physician of Liege ; who maintained, that 

 having tried the experiment, he found the sun's image, when the sky 

 was clear, to be round and not oblong ; and he ascribed the elongation 

 noticed by Newton, to the effect of clouds. Newton for some time 

 refused to reply to this contradiction of his assertions, though obsti- 

 nately persisted in ; and his answer was at last sent, just about the 

 time of Linus's death, in 1675. But Gascoigne, a friend of Linus, still 

 maintained that he and others had seen what the Dutch physician had 

 described ; and Newton, who was pleased with the candor of Gas- 



