ON GOETHE'S SCIENTIFIC RESEARCHES. 37 



colour is derived solely from a change in the proportions in 

 which light is mixed, and is, therefore, a property of light, not 

 of the coloured bodies, which only furnish an occasion for its 

 manifestation. 



A prism refracts transmitted light; that is to say, deflects it 

 BO that it makes a certain angle with its original direction; the 

 rays of simple light of different colours have, according to 

 Newton, different refrangibilities, and therefore, after refraction 

 in the prism, pursue different courses and separate from each 

 other. Accordingly a luminous point of infinitely small dimen- 

 sions appears, when seen through the pi-ism, to be first displaced, 

 and, secondly, extended into a coloured line, the so-called pris^ 

 matic spectrum, Avhich shows what are called the primary 

 colours in the order above-named. If, however, you look at a 

 broader luminous surface, the spectra of the points near the 

 middle are superposed, as may be seen from a simple geometrical 

 investigation, in such proportions as to give white light, except 

 at the edges, where certain of the colours are free. This white 

 surface appears displaced, as the luminous point did; but in- 

 stead of being coloured throughout, it has on one side a margin 

 of blue and violet, on the other a margin of red and yellow. A 

 black patch between two bright surfaces may be entirely covered 

 by their coloured edges; and when these spectra meet in the 

 middle, the red of the one and the violet of the other combine 

 to form purple. Thus the colours into which, at first sight, it 

 seems as if the black were analysed are in reality due, not to 

 the black strip, but to the white on each side of it. 



It is evident that at the first moment Goethe did not recol- 

 lect Newton's theory well enough to be able to find out the 

 physical explanation of the facts I have just glanced at. It was 

 afterwards laid before him again and again, and that in a 

 thoroughly intelligible form, for he speaks about it several times 

 in terms that show he understood it quite correctly. But he is 

 still so dissatisfied with it that he persists in his assertion that 

 the facts just cited are of a nature to convince any one who 

 observes them of the absolute incorrectness of Newton's theory. 

 Neither here nor in his later controversial writings does he ever 



425182 



