434 Proceedings of the British Association. 



poration ceased. The diurnal fluctuations were also shown to be the 

 least, when the irregular were the greatest (as observed by Mr. Birt), 

 because rain was then produced, and evaporation prevented from cool- 

 ing the air at the regular diurnal period, and in that way prevented the 

 rise of the barometer at that recurring period. 



Mr. Byrne gave an account of a new proportional Compass, which 

 by a vernier at the centre, and a means of adjusting the points, could, 

 by the aid of tables, multiply, divide, and compare lines, surfaces, solids, 

 and angles, with considerable precision. 



Friday. 

 Section B.— CHEMISTRY AND MINERALOGY. 



' On a peculiar .Condition of Zinc, produced by a long continued high 

 temperature,' by Dr. Tilley. — Dr. Tilley presented a specimen of zinc, 

 which had undergone a remarkable change in its arrangement, from 

 being kept at a heat above that of fusion for a considerable time. This 

 change was thought to bear some analogy to the alterations which 

 sulphur and some other bodies are known to undergo at different tem- 

 peratures. The condition of the zinc was singularly crystalline. The 

 zinc in this state was found to have the same chemical condition as the 

 ordinary zinc of commerce, and, although its oxides and salts had not 

 been examined, it was found, that when distilled, the zinc was restored 

 to its original texture. It was suggested, that many interesting examples 

 of similar molecular changes in other metals might be detected by sub- 

 jecting them to similar conditions to those in which this sample of zinc 

 was placed. 



Mr. Patterson entered into an explanation of his process, by which 

 silver was separated from lead, and stated, that he had observed similar 

 molecular changes in those metals. 



Report on a Hydrogen Furnace for Vitrification, and other applica- 

 tions of Heat in the Laboratory,' by the Rev. W. V. Harcourt.— At 

 the request of the British Association, Mr. Harcourt had undertaken 

 some years since to make experiments on vitrification. Dr. Faraday, in 

 his experiments on glass, had the greatest difficulty in procuring perfect- 

 ly homogeneous masses, arising in most cases from the almost impossi- 

 bility of procuring a regulated heat in the ordinary furnaces. Mr. Har- 

 court, impressed with the advantages which might be gained for optical 

 purposes, by procuring glasses formed by other salts and bases, institut- 

 ed some experiments with a view of ascertaining this point. It was 

 considered, that if a tnbasic phosphate formed a glass, and the bibasic 

 phosphate formed a glass, we should have, in all probability, glasses 



