GOETHE'S "FARBEXLEHRE." 63 



the experimental conditions. It is the power of in- 

 terpretation that he lacks. He flaunts this error re- 

 garding achromatism incessantly in the face of Newton 

 and his followers. But the error, which was a real one, 

 leaves Xewton's theory of colours perfectly unim- 

 paired. 



Xewton's account of his first experiment with the 

 prism is for ever memorable. " To perform my late 

 promise to you," he writes to Oldenburg, " I shall with- 

 out further ceremony acquaint you, that in the year 

 1666 (at which time I applied myself to the grinding 

 of optick-glasses of other figures than spherical) I pro- 

 cured me a triangular glass prism, to try therewith the 

 celebrated phenomena of colours. And in order thereto, 

 having darkened my chamber, and made a small hole 

 in my window-shuts, to let in a convenient quantity of 

 the sun's light, I placed my prism at its entrance, that 

 it might be thereby refracted to the opposite wall. It 

 was at first a very pleasing divertisement, to view the 

 vivid and intense colours produced thereby; but after 

 a while applying myself to consider them more circum- 

 spectly, I became surprised to see them in an oblong 

 form, which according to the received laws of refrac- 

 tions, I expected should have been circular. They were 

 terminated at the sides with straight lines, but at the 

 ends the decay of light was so gradual, that it was diffi- 

 cult to determine justly what was their figure, yet they 

 seemed semi-circular. 



" Comparing the length of this coloured spectrum 

 with its breadth, I found it about five times greater; a 

 disproportion so extravagant, that it excited me to a 

 more than ordinary curiosity of examining from whence 

 it might proceed." This curiosity Newton gratified 

 by instituting a series of experimental questions, the 

 answers to which left no doubt upon his mind that the 



