5288 M. Humboldt on the Temperature of Mines in America. 
Temperature. Depth in Feet. 
In the open air, - - to 10®.8 0 
In tlie Mina de Guadalupe, - 57 .7 unknown. 
Water of the mine, - - 52 .2 
In the Mina Purgatorio, which is extremely dry, the air was 
67^.3, Such a temperature in the interior of the earth, and 
almost at the height of the Peak of TenerilFe, is undoubtedly 
very remarkable. The thermometer in these countries stands 
at from 41° to 48^ in the day-time, and from 32^.7 to 35®. 6 
in the night. The point where I measured the temperature at 
Purgatorio, is nearly thirty toises lower than that of Guada- 
lupe. It is almost impossible to determine the depth relative 
to the surface of the earth, because the insulated mountain in 
which the mines are wrought, has a very irregular declivity. 
It is sufficient to recollect that the levels of the two mines are 
a little above the level of the Plateau of Micuipampa, and from 
250 to 300 toises below the summit of the Mountain Hual- 
gayoc. 
Two points in the interior of this mountain of 1840 toises of 
absolute height, have therefore 57®. 7 and 67®. 3 of temperature. 
When the surrounding air has a mean temperature of 46®, the 
water of the mines is in the same places 52®. 2. 
AiiT. XII . — On the Ellipticiiy of the Earth. Ey William 
Watts, Esq. Communicated b)^ the Author. 
Problem. T- O determine the ellipticity of the Earth, and 
the increase of gravity from the equator to the poles, on the hy- 
jxitliesis, that the greatest error in the observations of the 
lengths of the seconds’ pendulum, is less than in every other 
elliptical figure, assuming for data the observations of the 
lengths of the seconds’ pendulum, made by Captain Kater, at 
the different points of tlie British meridian, from Unst to Dun- 
nose, as stated in the table published in this Journal, vol. ii. 
p. 321 
* In Captain Katei’s experiments on the pendulum, ordered by the House of 
Commons to be printed, tlie \ ihrations for London in a mean solar day are stated at 
8()0d9.21. 
