Specimens of Sir James Hall's Experiments. 215 



miles. Column VII. Compressing force, expressed in atmo- 

 spheres. 



Boih tables were computed separately, by a friend, Mr. 

 J. Jaidine, and myself. 



The following data were employed : 



Area of a circle of which the diameter is unity, 0*785398. 



Weight of a cubic foot of distilled water, according to 

 professor Robison, 998-74 ounces avoirdupois. 



Mean specific gravity of sea water, according to Bladh, 

 1-0272. 



Mean heioht of the barometer at the level of the sea 

 29'9119G English inches, according to Laplace. 



Specific gravity of mercury, according to Cavendish and 

 Brisson, 13-568. 



XXXIII. Catalogjie of Specimens, showing the Result of 

 Sir James Hall's Experiments on the Effects of Heat ' 

 modified by Compression ; which were deposited by Sir 

 James Hall in the British Museum on the 2Slh of June 

 1S06. 



IN umbers 1, 2, 3, 4, 5, 6, and 7, were all produced, in 

 separate experiments, from pounded carbonate of lime. 

 No. 1. was obtained in 1799- It is a firm stone, requiring 

 a smart blow of a hammer to break it. It was enclosed in 

 a cartridge of paper, the mark of which it still bears. The 

 other six are still harder, and more compact, approaching 

 nearly in these qualities to common limestone. 



Nos. 2, 4, and 7, possess a degree of s"mi -transparency 

 most remarkable in No. 4 ; and all of these specimens ex- 

 hibit an uneven fracture, approaching to that of bees' wax 

 and marble. Their colours are variously, though slightly, 

 tinged with yellow and blue ; in particular No. 3, which, 

 though produced from common white chalk, resembles a 

 y< How marble. 



Nos. 3, 5, and 6, have taken a tolerable polish. No. 7. 

 contains a shell introduced along with the pounded chalk, 

 and now closely incorporated with it. 



O 4 .Mono: 



