Proceedings of the Polytechnic Association. 805 



Dr. J. J. Edwards remarked that he liad seen a paint like this 

 used in frescoing, over thirty years ago, but it was found not to be 

 durable. 



Mr. Hodgeson replied that the cause of that paint not being 

 durable, was on account of its being composed chiefly of soluble 

 gla,6s, which would not stand, for any length of time, the action of 

 the atmosphere. He had coated every kind of surface with his paint, 

 and exposed them to very severe tests, without any preceptible 

 change for years. This paint will cost about three-fourths less than 

 the ordinary paint. The artificial stone made of oxalate of lime, 

 alum and sand, was found to be insoluble in boiling water. 



Dr. P. H. Yanderweyde said that all the salts of soda, are 

 exceedingly soluble, so, when they are combined with silex, they 

 form soluble silex. Water-glass, when first used as a paint, was 

 prepared by boiling potash with sand to the consistency of syrup ; 

 but this preparation was found to contain too much soda, which was 

 easily affected by moisture. And this is the objection to soluble 

 glass as a paint, the soda will not stand the influence of the weather. 



Prof. Phin remarked that the French have used oxalic acid in the 

 same way as stated; the acid being afterward washed with sulphuric 

 acid. A full account of this process can be found in the Comptes 

 Rendes. This shows that the principle has been used in France 

 some time since, and has been well spoken of there. 



Light and Color. 

 Di". P. H. Yanderwej'de gave an elaborate and interesting lecture 

 on light and color, descriptive of the spectra of different gases, 

 fluids, etc., and the manner in wdiich the elemental constituents of 

 solar bodies have been ascertained. He also explained the causes of 

 the difference of color in various bodies of organic origiu, as, for 

 instance, the mother-of-pearl, which is secreted in the interior of 

 shells and made up of translucent laminae, the irregular surfaces of 

 which break up tlie rays of light, and cause the development of color 

 in the same manner that a similar result is produced when a glass 

 surface is closely lined with a diamond point. 



Hemisphere Model of the Moon. 

 • Mr. Charles B. Boyle presented a carefully executed model of that 

 side of the moon which is visible to us. He has used in his authori- 

 ties Behr and Midler's femous lunar map, and the photographs of 



