408 Intelligence and Miscellaneous Articles. 



equally applicable here, as are also the same contrivances for pho- 

 tographic registry, with trifling alterations corresponding to the dif- 

 ference between expansion and condensation of gas. 



Having alluded to the application of convex lenses to increase the 

 sensitiveness of actinometers, I may as well add that, to avoid the 

 concentration of heat as well as light, we must, at least when opera- 

 ting with the sun's rays, make them pass, either before entering or 

 after leaving the lens, through some medium which will intercept (or 

 metamorphose) the heat rays, e. g. blue glass or coloured solutions, 

 or some one of those salts (either solid or in solution) which are 

 known for their adiathermic properties, or else we may have the lens 

 itself constructed of one of these substances. 



In conclusion, the amount of success which has already attended 

 the efforts to measure what we may for convenience call the cyanic 

 actinism, suggests the desirableness of attempts being made to obtain 

 some similar system of registry (either by properly prepared papers, 

 or liquids, or gases) of the strength of that opposite influence lower 

 down in the spectrum which has been made known to us by Dr. 

 Draper and Mr. R. Hunt ; and our success thus far may then suggest 

 further the possibility of our being able separately to identify and to 

 contrive some measurement for some of the many other powers pro- 

 bably contained in the light of the sun and other luminaries, both as 

 originally emitted, and as altered by reflexion or transmission. 



ARSENIC IN COAL. 



At a recent meeting (Oct. 16) of the Manchester Literary and 

 Philosophical Society, Dr. R. Angus Smith gave a short account of 

 his examination of coal pyrites for arsenic. He stated that although 

 the knowledge of the existence of arsenic in the iron pyrites found 

 in coal may not be considered perfectly novel, it certainly does not 

 seem to be known that arsenic is so widely disseminated as to form 

 an ordinary constituent of the coals burnt in our towns ; and chemists 

 of celebrity have held, and now hold, it to be absent there. He 

 had examined fifteen specimens of coal in Lancashire, and found 

 arsenic in thirteen. He had also found it in a few others ; but Mr. 

 Binney having promised a collection, properly arranged, the exa- 

 mination will then be made more complete. Mr. Dugald Campbell 

 had also lately found arsenic in coal pyrites ; this had a very direct 

 bearing on our sanitary knowledge, as we must now be obliged to 

 add arsenic to the number of impurities in the atmosphere of our 

 large towns. It is true that he had not actually obtained it from the 

 atmosphere ; but when the pyrites is burnt the arsenic burns and is 

 carried off along with the sulphur. One or two coal brasses (as they 

 are called) contained copper, a metal that is also to some extent 

 volatilized, as may be readily observed wherever copper- soldering 

 takes place. Although an extremely small amount of copper is car- 

 ried up from furnaces, it is not well entirely to ignore it. The 

 amount of arsenic, however, is probably not without considerable 

 influence ; and we may probably learn the reason why some towns 

 seem less affected than others by the burning of coals, by examining 

 the amount of arsenic burnt as well as sulphur. 



