GOETHE'S "FAKBEXLEHRE." 55 



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 behind, so that the light shone, 

 not on but through the turbid liquid, the blue colour 

 disappeared, and he had yellow in its place. Such 

 experiments are capable of endless variation. To this 

 class of effects belongs the painter's "chill." A cold 

 bluish bloom, like that of a plum, is sometimes observed 

 to cover the browns of a varnished picture. This is 

 due to a want of optical continuity in the varnish. 

 Instead of being a coherent layer it is broken up into 

 particles of microscopic smallness, which virtually con- 

 stitute a turbid medium and send blue light to the 

 eye. 



Goethe himself describes a most amusing illustra- 

 tion, or, to use his own language, "a wonderful phenome- 

 non,'' due to the temporary action of a turbid medium 

 on a picture. " A portrait of an esteemed theologian was 

 painted several years ago by an artist specially skilled 

 in the treatment of colours. The man stood forth in 

 his dignity clad in a beautiful black velvet coat, which 

 attracted the eyes and awakened the admiration of the 

 beholder almost more than the face itself. Through 

 the action of humidity and dust, however, the picture 

 had lost much of its original splendour. It was there- 

 fore handed over to a painter to be cleaned, and newly 

 varnished. The painter began by carefully passing a 

 wet sponge over the picture. But he had scarcely thus 

 removed the coarser dirt, when to his astonishment the 

 black velvet suddenly changed into a light blue plush; 

 the reverend gentleman acquiring thereby a very worldly, 

 if, at the same time, an old-fashioned appearance. The 



