■308 *''Wf}j^^'?)wfAe [Aphil, 



Here A = 57 



a = 0-0694 



B = 1 



b = 0-00824 and 



a = 



A a + B ft n-95S3 + 0-00824 3-96657 



A + B 58 58 



= 0-06838. 



Here the error is 0-0106, or almost l-65th part, by which the 

 hydrogen gas is too light. But, at the same temperature, com- 

 mon air saturated with moisture is about l-58th part too light. 

 These two errors do not quite correct each other ; but they ren- 

 der the specific gravity of the hydrogen gas somewhat higher 

 t^an the truth; for 0-9829 : 1 :: 0-06838 : 0-06956 = sp. gr. of 

 hydrogen gas taken in this way. This exceeds the truth about 

 1 -600th part. We see from it that the specific gravity of hydro- 

 gen gas should be taken at as low a temperature as possible. 



I have little doubt that the specific gravity of hydrogen gas 

 found by Berzehus and Dulong ; namely, 0-0688, was a little too 

 .^light, in consequence of the presence of the vapour of water in 

 it. To prevent the vapour of water from mixing with their gas, 

 they covered the surface of the water in the trough with oil. 

 ^But if the gas, when produced, passed through water, as it 

 obviously must have done, this precaution could not have 

 answered the end intended. It is obvious that the presence of 

 vapour, instead of augmenting the specific gravity of the gases, 

 would have diminished it. The error then in the determination 

 of the specific gravity of hydrogen gas by Biot and Arago, did 

 not proceed from the presence of vapour ; but from, the presence 

 of a small quantity of common air. 



Article VIII. 



Observations on the Temperat^ire of Mines in Cornwall. 

 By Mr. M. P. Moyle. 



(To the Editor of the Annals of Philosophy.) 



SIR, * Helstoii^ March 16, 1822. 



Mr. Fox having communicated to the editors of the Annales 

 de Chimie et de Physique new determinations on the tempera- 

 ture of the earth at various depths, these gentlemen have pub- 

 lished them, along with an extract made by M. Fourier, from his 

 •profound geometrical researches on heat. 



Mr. Fox's observations were made in 10 different mines in this 

 ^ounty from the depth of 10 fathoms to that of 240 fathoms, at in- 

 tervals of lOfathoms from each observation ; and^ according to his 



i 



