LAW OF DISPERSION BY REFRACTION. G3 



.ess bordered with color, in consequence of this property. The im- 

 provement of telescopes was, in Newton's time, the great practical 

 motive for aiming at the improvement of theoretical optics. Newton's 

 theory showed why telescopes were imperfect, namely, in consequence 

 of the different refraction of different colors, which produces a chro- 

 matic aberration : and the theory was confirmed by the circumstances 

 of such imperfections. The false opinion of which we have already 

 spoken, that the dispersion must be the same when the refraction is 

 the same, led him to believe that the imperfection was insurmountable, 

 that achromatic refraction could not be obtained : and this view 

 made him turn his attention to the construction of reflecting instead 

 of refracting telescopes. But the rectification of Newton's error was 

 a further confirmation of the general truth of his principles in other 

 respects ; and since that time, the soundness of the Newtonian law of 

 refraction has hardly been questioned among physical philosophers. 



It has, however, in modern times, been very vehemently contro- 

 verted in a quarter from which we might not readily have expected a 

 detailed discussion on such a subject. The celebrated Gothe has writ- 

 ten a work on The Doctrine of Colors, (Farbenlehre ; Tubingen, 1810,) 

 one main purpose of which is, to represent Newton's opinions, and the 

 work in which they are formally published, (his Opticks,) as utterly 

 false and mistaken, and capable of being assented to only by the most 

 blind and obstinate prejudice. Those who are acquainted with the 

 extent to which such an opinion, promulgated by Gothe, was likely to 

 be widely adopted in Germany, will not be surprised that similar 

 language is used by other writers of that nation. Thus Schelling 15 



O O / 



says : " Newton's Opticks is the greatest proof of the possibility of a 

 whole structure of fallacies, which, in all its parts, is founded upon 

 observation and experiment." Gothe, however, does not concede even 

 so much to Newton's work. He goes over a large portion of it, page 

 by page, quarrelling with the experiments, diagrams, reasoning, and 

 language, without intermission , and holds that it is not reconcileable 

 with the most simple facts. He declares, 18 that the first time he 

 looked through a prism, he saw the white walls of the room still look 

 white, "and though alone, I pronounced, as by an instinct, that the 

 Newtonian doctrine is false." We need not here point out how incon- 

 sistent with the Newtonian doctrine it was, to expect, as Gothe 

 expected, that the wall should be all over colored various colors. 



Vorlcxungen, p. 270. " Farbenlehre, vol. ii. p. 678. 



