It322.] Difference in the Specific Gravity of Bodies, 41^; 



of a volume of air by one degree. Then ^ — T will express the 

 difference of temperature between the atmosphere and the heated 

 column. If, therefore, the volume at T be called 1, that at one 

 degree above will be 1 + e, and that at ^ — T will be 



Then since the densities will be inversely as the vnlnp g p g we 

 have as D : ^ :: (1 + ej-' : 1. ■^^'^mm^ 



Hence D - d! = 1 - —1- t - Tand?; = 2 p;^ h^ '^ 



(l — ■ , ^^ •— T.j The temperature of a chimney being 120^;' 



that of the outer air 40°, and the height of the chimney 40 feefcl^ 

 what will be the velocity of the current ? 



lathis case, c=2x4x^/40xl- ^^^55^5 = 7-7364. 



In getting the denominator of the fraction, it may be convenient, 

 to have the logarithm of 1-00208, which is -0009038. 



I am, yours truly, 



C. Sylvester. 



Article V. ^ 



'it 

 On the Temperature of Mines in Cornwall. By Mr. M. P. Moyle. 



(To the Editor of the Annals of Philosophy.) 



SIR, IJelston, Ma^ 3 ylS22. 



When I asserted in the Annals of Philosophy for April last" 

 that Mr. Fox had drawn false conclusions as regards the temper- 

 ature of mines in this county, the impression on my mind was, 

 that sufficient attention had not been paid to the selection of 

 spots free from doubtful causes, but he assures us in your last 

 number that every precaution was made to obviate such effects. 

 I hope this was the case ; as I am fully convinced from the expe- 

 riments which I have made, that it is otherwise impossible to 

 get near the truth ; and I most sincerely hope that Mr. Fox does 

 not feel offended at any remarks of mine which may be in oppo- 

 sition to his own, as I conceive it is only by the colhsion of facts 

 by different individuals that the truth can be elucidated. 



I would now remark that unless we can select spots where 

 workmen have no access, and where the air and water are in a 

 state of rest, it will be impossible to gain the truth. A favourable 

 opportunity of this description occurred to me five days since in: 

 Wheal Trenoweth Mine, 100 fathoms east of Crenver and Oat- 

 field Mines on the same load. This mine has discontinued 

 working (I beheve) for more than 12 months, or at least as far 



