ON goethe's scientific researches. 57 



simply a geometrical point, in which the reflected rays, 

 if produced backwards, would intersect. And, accordingly, 

 no one expects the image to produce any real effect 

 behind the mirror. In the same way the prism shows 

 us images of objects which occupy a different position 

 from the objects themselves ; that is to say, the light 

 which an object sends to the prism is refracted by it, so 

 that it appears to come from an object lying to one side, 

 called the image. This image, again, is not real ; it is, as 

 in the case of reflection, the geometrical point in which 

 the refracted rays intersect when produced backwards. 

 And yet, according to G-oethe, this image is to produce 

 real effects by its displacement ; the displaced patch of 

 light makes, he says, the dark space behind it appear 

 blue, just as an imperfectly transparent body would, and 

 so again the displaced dark patch makes the bright space 

 behind appear reddish-yellow. That Goethe really treats 

 the image as an actual object in the place it appears to 

 occupy is obvious enough, especially as he is compelled 

 to assume, in the course of his explanation, that the 

 blue and red edges of the bright space are respectively 

 before and behind the dark image which, like it, is 

 displaced by the prism. He does, in fact, remain loyal 

 to the appearance presented to the senses, and treats a 

 geometrical locus as if it were a material object. Again, 

 he does not scruple at one time to make red and blue 

 destroy each other, as, for example, in the blue edge of a 

 red surface seen through the prism, and at another to 

 construct out of them a beautiful purple, as when the 

 blue and red edges of two neighbouring white surfaces 

 meet in a black ground. And when he comes to Newton's 

 more complicated experiments, he is driven to still more 

 marvellous expedients. As long as you treat his explana- 

 tions as a pictorial way of representing the physical 

 processes, you may acquiesce in them, and even frequently 



