SU Professor Tyndall [March 19, 



colours being confined to the edges. Goethe's earliest experiment, 

 which led him so hastily to the conclusion that Newton's theory of 

 colours was wrong, consisted in looking through a prism at the white 

 wall of his own room. He expected to see the whole wall covered 

 with colours, this being, he thought, implied in the theory of Newton. 

 But to his astonishment it remained white, and only when he came to 

 the boundary of a dark or a bright space did the colours reveal them- 

 selves. This question of "boundaries" is one of supreme importance 

 to the author of the ' Farbenlehre ' ; the end and aim of his theory 

 being to account for the coloured fringes produced at the edges of his 

 refracted images. 



Darkness, according to Goethe, had as much to do as light with 

 the production of colour. Colour was really due to the commingling 

 of both. Not only did his white rectangles upon a black ground 

 yield the coloured fringes, but his black rectangles on a white ground 

 did the same. The order of the colours seemed, however, different in 

 the two cases. Let a visiting card, held in the hand between the eye 

 and a window facing the bright firmament, be looked at through a 

 prism, then supposing the image of the card to be shifted upwards by 

 refraction, a red fringe is seen above and a blue one below. Let the 

 back be turned to the window and the card so held that the light 

 shall fall upon it ; on being looked at through the prism, blue is seen 

 above and red below. In the first case the fringes are due to the 

 decomposition of the light adjacent to the edge of the card, which 

 simply acts as an opaque body, and might have been actually black. 

 In the second case the light decomposed is that coming from the 

 surface of the card itself. The first experiment corresponds to that 

 of Goethe with a black rectangle on a white ground ; while the 

 second experiment corresponds to Goethe's white rectangle on a black 

 ground. Both these effects are immediately deducible from Newton's 

 theory of colours. But this, though explained to him by physicists 

 of great experience and reputation, Goethe could never be brought to 

 see, and he continued to affirm to the end of his life that the results 

 were utterly irreconcilable with the theory of Newton. 



In his own explanations Goethe began at the wrong end, invert- 

 ing the true order of thought, and trying to make the outcome of 

 theory its foundation. Apart from theory, however, his observations 

 are of great interest and variety. He looked to the zenith at mid- 

 night, and found before him the blackness of space, while in daylight 

 he saw the blue firmament overhead ; and he rightly adopted the 

 conclusion that this colouring of the sky was due to the shining of 

 the sun upon a turbid medium with darkness behind. He by no 

 means understood the physical action of turbid media, but he made 

 a great variety of experiments bearing upon this point. Water, for 

 example, rendered turbid by varnish, soap, or milk, and having a black 

 ground behind it, always appeared blue when shone upon by white 

 light. When, instead of a black background, a bright one was placed 

 behin<l, so that the light shone, not on, but tlirougli the turbid 



