448 Mr. Moyle on the Depression of the Barometer. [Dee: 
from the bottom of several deep mines, I find it, in most in-~ 
stances, to contain in solution a very minute quantity of any’ 
foreign substance, varying, perhaps, from one to five or six | 
grains ina pint. Its relative purity appears to have no reference } 
to the depth or temperature of the mines; for instance, Huel ) 
Abraham, and Dolcoath, are the two deepest, and two of the 
warmest mines in the county; and the water from the bottom of 
these mines does not, in either case, hold in solution more than 
about two grains of foreign matter in a pint. On the other hand, 
some mines abound with much less pure water. That from the 
Consolidated Mines leaves 10 grains of residuum from a pint; 
Huel Unity, 16 grains; from one shaft in Poldice, 19; and 
from another 92 grains, from the same quantity. In most of the 
mine-water that I have examined, the muriatie salts, especially 
the muriates of lime and of iron, are most abundant. I have 
detected muriate of soda in some instances, particularly in the 
water from the bottom of the United Mines, the Consolidated 
Mines, Huel Unity, and Poldice. | ew 
Out of the 92 grains of residuum produced from a pint of 
water from one of the engine shafts of the latter mine, 24 grains 
proved to be the muriate of soda, 52 grains the muriates of lime 
and magnesia, chiefly the former, and the remainder muriate of 
iron, and a small quantity of the sulphate of lime. 
- The water from another engine shaft of the same mine con- 
tained 51 grains of muriate of soda, and about 13 grains of the 
muriates of lime and magnesia, and the carbonated oxide of 
iron. All the mines above enumerated are situated in the inte- 
rior of this part of Cornwall, and are distant several miles from 
the sea! 
en ee ee 
ArtTic.e VII. 
On the Depression of the Barometer in Dee. 1821. | 
By M. P. Moyle, Esq. 
(To the Editor of the Annals of Philosophy.) 
SIR, Helston, Nov. 6, 1822. 
PERCEIVING a wish of Prof. Brandes in the Annals for Oct. 
that every particular relative to the great depression of the mer- 
cury in the barometer in Dec. 1821, might be minutely detailed 
as it occurred in England, I beg to give my observations begin~ 
ning with the 24th of the month. 
