564 Glironicles of Science. [Oct, 



11. PHYSICS. 



Light. — A diaphanometer to determine the transparency of different 

 kinds of glass has been de^dsed by M. Jicinsky. \\'ithout the 

 engravings, it is impossible to make this instrument understood. The 

 author has proved that the diaphanicity of divers kinds of glass is 

 not dependent so much on its chemical composition, as on certain 

 physical properties due to the heat apphed in making it. 



Physicists and others engaged in optical studies will feel in- 

 terested in hearing that there has been a discovery of large crystals 

 of quartz in a difficultly accessible portion of the Swiss Alps ; one of 

 these weighs 267 lbs., is 69 centimetres in height, and has a cir- 

 cumference of 122 centimetres. 



The employment of the spectroscope to distinguish a feeble 

 light present with a stronger light, has been suggested by M. Seguin. 

 The author describes a series of experiments with electric light, and 

 observations thereon with Duboscq's vertical spectroscope. The 

 conclusion arrived at is that the spectroscope eminently serves the 

 purpose of detecting a feeble light present along with a much 

 stronger one, the former of which would be invisible to the naked 

 eye, or by means of other oj)tical instruments. 



The zirconia light is attracting great attention on the Continent. 

 The chief desideratum in oxyhydrogen illumination of this kind is 

 the cheap production of oxygen ; and the process of M. Tessie du 

 Mothay, according to the Paris correspondent of the ' British 

 Journal of Photography,' appears to be all that can be desired so 

 far as cheapness and efficacy are concerned. It consists in heating 

 in iron retorts, divided in two by a horizontal grating, a quantity 

 of manganate of soda. This is raised to a dull red heat, and a 

 current of superheated steam is made to pass over the mass. 

 Oxygen is given off in abundance and passes along with the current 

 of steam into a refrigerator, where the steam is condensed into 

 water, and the oxygen is afterwards collected in a gasometer. The 

 next operation is to re-oxygenize the exhausted manganate. This 

 is accomplished by passing heated atV, not steam, over it, when the 

 manganate absorbs the oxygen, and becomes as ready as ever for 

 yielding it again to the vapour of water. Thus the two operations 

 can go on for an indefinite time, the air being the source of supply 

 of oxygen. One advantage claimed by the advocates of the zirconia 

 cylinders, besides their durability, is that a mixture of equal parts 

 of oxygen and carburetted hydrogen can be used instead of a mix- 

 ture in which oxygen is in excess, as is usual. There are large 

 oxygen gas works for carrying out this method now erected in New 

 York. The essential portions of the process are carried on by the 

 aid of brick furnaces, of which only one was in operation at the 



