On Underground Temperatures, 



3 



The subject of underground temperature is far from being new. It 

 attracted attention a century and a-half ago, some observations 

 having been made by Gensanne in 1740 in the mines of Alsace, 

 which if we take the mean annual temperature at the mines of 47° F., 

 give, curiously enough, an increase of 50 feet per degree Fahr. 



Towards the end of the century, a few experiments were made by 

 Saussure in Switzerland, and by Humboldt in America, but the 

 more important ones were those made by Daubuisson in 1803, in the 

 mines of Saxony and France, which gave a rate of increase varying 

 from 54 to 72 feet per degree F. De Trebra carried on similar ob- 

 servations in one of the Saxony mines for two years, which, taking 

 the surface temperature at 44°, show an increase of 57 feet per 

 1° Fahr. 



Passing over some minor observations, we come to the series of 

 careful and systematic observations commenced in Cornwall by 

 Dr. Forbes and by Mr. R. Were Fox, about 1820, and which were 

 carried on by the latter continuously until 1857. Other Cornish 

 geologists followed, Mr. W. J. Henwood especially, who between 

 1837 and 1858, made a large number of experiments, not only in 

 Cornwall, but also in the mines of South America. Notwithstanding 

 that the instruments had not the perfection of those of later date, the 

 observations are of great value, as they were conducted under very 

 varied conditions, and with a full understanding of the various 

 causes of interference to be guarded against. They show very con- 

 siderable variations in the rate of increase with depth. Mr. Fox 

 records a range for 1° F. of from 32 to 70 feet, from which De la 

 Beche deduced a mean from 46 to 51 feet ; and Henwood, while finding 

 the results to range as widely as did Mr. Fox, nevertheless estimated 

 from a large number of averages the gradient for 1° F. to be from 

 37 to 41 feet only. 



In 1822, Cordier published his celebrated " Essai sur la Tempera- 

 ture de l'lnterieur de la Terre," and in this he recorded the observa- 

 tions previously made by Gensanne, Daubuisson and Fox, together 

 with some observations made by himself in the coal-pits of France. 

 The several results showed variations extending from 13 to 57 metres 

 per 1° C, but he concluded the mean to be about 1° C. per 25 metres 

 of depth. 



Amongst the most careful of the early observations are those made 

 by De la Rive and Marcet in an artesian well at Pregny near Geneva. 

 In this case, the thermometer was protected against pressure, and the 

 result gave a rate of increase of 48J feet per 1° F. 



This was shortly followed by Professor Phillip's well-known 

 observations in the deep coal-pit of Monkwearmoufch, Sunderland ; 

 great precautions were taken against error, and in the result an in- 

 crease of 1° for every 62 feet of depth was obtained. 



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