222 THE POPULAR SCIENCE MONTHLY. 



out of such meager elements as his yellow, and his blue, and his turbid 

 medium, did he extract the amazing variety and richness of the New- 

 tonian spectrum ? Here we must walk circumspectly, for the intellec- 

 tual atmosphere with which Goethe surrounds himself is by no means 

 free from turbidity. In trying to account for his position, we must 

 make ourselves acquainted with his salient facts, and endeavor to place 

 our minds in sympathy with his mode of regarding them. He found 

 that he could intensify the yellow of his transmitted light by making 

 the turbidity of his medium stronger. A single sheet of diaphanous 

 parchment placed over a hole in his window-shutter appeared whitish. 

 Two sheets appeared yellow, which by the addition of other sheets 

 could be converted into red. It is quite true that by simply sending 

 it through a medium charged with extremely minute particles we can 

 extract from white light a ruby red. The red of the London sun, of 

 which we have had such fine and frequent examples during the late 

 winter, is a case to some extent in point. Goethe did not believe in 

 Newton's differently refrangible rays. He refused to entertain the 

 notion that the red light obtained by the employment of several sheets 

 of parchment was different in quality from the yellow light obtained 

 with two. The red, according to him, was a mere intensification 

 " Steigerung " of the yellow. Colors in general consisted, accord- 

 ing to Goethe, of light on its way to darkness, and the only difference 

 between yellow and red consisted in the latter being nearer than the 

 former to its final goal. 



But how in the production of the spectrum do turbid media come 

 into play ? If they exist, where are they ? The poet's answer to this 

 question is subtile in the extreme. He wanders round the answer 

 before he touches it, indulging in various considerations regarding pe- 

 numbra? and double images, with the apparent aim of breaking down 

 the repugnance to his logic which the mind of his reader is only too 

 likely to entertain. If you place a white card near the surface of a 

 piece of plate-glass, and look obliquely at the image of the card re- 

 flected from the two surfaces, you observe two images, which are hazy 

 at the edges and more dense and defined where they overlap. These 

 hazy edges Goethe pressed into his service as turbid media, He fan- 

 cied that they associated themselves indissolubly with his refracted 

 rectangles that in every case the image of the rectangle was accom- 

 panied by a secondary hazy image, a little in advance of the principal 

 one. At one edge, he contended, the advanced secondary image had 

 black behind it, which was converted into blue ; while at the other 

 edge it had white behind it, and appeared yellow. When the refracted 

 rectangle is made very narrow, the fringes approach each other and 

 finally overlap. Blue thus mingles with yellow, and the green of the 

 spectrum is the consequence. This, in a nutshell, is the theory of 

 colors developed in the " Farbenlehre." Goethe obviously regarded 

 the narrowing of the rectangle, of the cylindrical beam, or of the slit 



