190 



until intercepted by solids or liquids. It follows that the air in which 

 clouds are situated, will be warmer than that above and below them. 



Thus radiant heat and electricity may promote their buoyancy; 

 nevertheless their persistency between two levels must be ascribed to 

 the process noticed on the summit of the Rhigi. 



Mr. Espy had the merit of drawing the attention of meteorologists 

 more strongly to the fact, previously made known by Dalton,* that, 

 although cold is produced by the rarefaction of air containing vapour, 

 yet the reduction of temperature is less, whenever the vapour is 

 condensed, than it would have been in air free from vapour. 



In adopting the explanation above given, Dr. Hare had been 

 prompted by his knowledge of Mr. Espy's suggestions founded on 

 those of Dalton, so far as a superior temperature had been ascribed 

 to the air containing a recent cloud. 



Mr. Boye made an oral communication relative to a white 

 crystalline mineral, which occurs three or four miles to the 

 south of West Chester, Pa., and which encloses corundum and 

 several other mineral species. 



The specimen was handed to him for examination by Mr. Nuttall, 

 several years since, and, proving to be a silicate closely allied to a 

 felspar, he subjected it to analysis, in conjunction with Prof. Booth, 

 in order to compare it with the several felspars previously investigated 

 by them. 



It forms a white translucent mass composed of densely aggregated 

 crystalline grains, and might be mistaken, at the first glance, for a 

 moderately coarse-grained marble, did not its hardness indicate a to- 

 tally different substance. Its specific gravity is 2.612. 



The analysis was performed in the manner mentioned in the Pro- 

 ceedings of the Society for May, 1841, and gave the following results: 



Oxygen. 



35.18 

 9.593 -J 



2 724 3 ' 101 j 



0.027 J 



* See Nicholson's Journal, vol. iii. p. 160, or Manchester Memoirs, vol. v. 

 p. 515. 



Silica, 



. , 



. 



67.72 



Alumina, with 



a trace of 



iron, 



20.54 



Magnesia, 



. 



. 



0.34 



Lime, 



. 



. 



0.78 



Soda, . 



. 



, 



10.65 



Potassa, . 







0.16 





100.19 



