GOETHE'S ' FAKBENLEHRE.' 63 



leaves Newton's theory of colours perfectly unim- 

 paired. 



Newton's account of his first experiment with the 

 prism is for ever memorable. 'To perform my late 

 promisejtp^y ou,' he writes to Oldenburg, c 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 

 difficult 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 

 elongation of his spectrum was due to the fact * that 

 light is not similar or homogeneal, but consists of 

 difform rays, some of which are more refrangible 

 than others ; so that, without any difference in their 



