Intelligence and Miscellaneous Articles. 389 



ceive the normal number of impulses, and after passing, the impulses 

 reach you less frequently. The shrill shriek, the real tone, and the 

 low roar in this case are facts which I suppose to be parallel to the 

 red, the white, and the blue light of a star moving swiftly, first 

 toward, and then from us. — Silliman's American Journal, September 

 1865. 



ON THE ACTION OF LIGHT UPON SULPHIDE OF LEAD, AND ITS 

 BEARING UPON THE PRESERVATION OF PAINTINGS IN PICTURE- 

 GALLERIES. BY DR. D. S. PRICE*. 



The author's attention was directed to this subject by observing 

 that in the cases in the South Kensington Museum, which are 

 painted with white lead, substances which emitted sulphurous 

 vapours did not cause a darkening of the surface of the case, except- 

 ing where it was protected from the direct influence of light. A 

 number of experiments were then tried as to the action of light upon 

 sulphide of lead produced by the action of sulphuretted hydrogen 

 upon lead paint. A board painted white with white-lead was ex- 

 posed for several hours to the action of sulphuretted hydrogen, until 

 the surface had acquired a uniform brown colour. Plates of glass 

 of different colours were then placed upon the painted surface, one 

 portion being at the same time covered with an opake medium, and 

 another left entirely exposed. The board was then placed facing 

 the light. The glasses employed were red, blue, yellow (silver), 

 violet, and smoke-colour glass. The results exhibited were after an 

 exposure of eight days, and showed that the parts of the board 

 directly exposed to light were bleached ; those protected by an 

 opake medium were not acted upon ; while with the glasses of dif- 

 ferent colours intermediate effects were produced, those of the violet 

 glass being most decided. Drying-oils in conjunction with light 

 rapidly bleach sulphide of lead, and boiled oil effects the bleaching 

 still more rapidly. When water-colour is used bleaching takes place, 

 but much more slowly than in the case of oil. After quoting autho- 

 rities, stating that generally light was advantageous to the preser- 

 vation of pictures, Dr. Price showed a striking illustration of this 

 fact. He had a picture painted, and then exposed it to the action of 

 sulphuretted hydrogen, until it became sadly discoloured, and to all 

 appearance destroyed. Some strips of paper were laid across the 

 picture so as to cover some parts. The picture, thus partially covered, 

 was exposed to light for a long time. The result, as shown at the 

 Meeting, was very curious indeed — the parts of the picture exposed 

 being perfectly restored, while those protected by the paper remained 

 still discoloured. From his experiments he came to the conclusion 

 that it was advantageous to have picture-galleries well lighted, espe- 

 cially where, as in towns, the atmosphere was charged with sulphur 

 compounds, and that it was quite a mistake to have curtains placed 

 in front of pictures with a view to their protection. In the course 

 of his communication, Dr. Price referred to the use of zinc paint for 



* From a communication read at the Meeting of the British Association, 

 Birmingham, September 1865. 



