406 



TRANSACTIONS OP*THE 



Cornwall, well authenticated, the temperature of the 

 pump water, when the mine was 510 feet deep, was 62°; 

 when the mine was 670 feet deep, it was 67°. 



Observations of a similar character have been made in 

 Germany, at one of the mines of Freyburg, which was 

 worked to the depth of 1200 feet and then abandoned in 

 a great measure; and the water consequently had greatly 

 accumulated: when the external air was 39° the tem- 

 perature of the water was 61°, which is about 10° above 

 the mean temperature of Freyberg. 



I recollect well, in 1828, making some experiments on 

 this subject at the mine of Valenciana, Mexico, at the 

 period that they had drained the water to the depth of 

 1500 feet ; and the water which was delivered at the 

 mouth of the shaft from that depth, was very much above 

 the temperature of the atmosphere. The precise number 

 of degrees, said to be 96 by Professor Millington, I regret 

 being unable to state, having unfortunately lost all my 

 papers when attacked by banditti, in the autumn of that 

 year, on the route from Mexico to Vera Cruz. As near 

 as I can remember, it fully corroborated the experi- 

 ments tried in England and Germany. 



The fact of this increase is so well sustained by the 

 experiments of Daubisson in the mines of Saxony and 

 France, by Patrin in Siberia, by Humboldt in South 

 America and by late investigators in England, that it will 

 be only necessary to give place to the following table 

 drawn up with much care by Cornish geologists. 



