On Underground Temperatures. 



5 



conditions of depth, strata, isolation, &c, under which they were 

 made. 



In the summary of results given in the Report for 1882, Professor 

 Everett, after describing the instruments used, the methods of obser- 

 vation, and the many questions affecting the value of the observa- 

 tions, such as the heat generated by the boring tools, or by chemical 

 action, the effects of ventilation, the convection of heat by air and 

 water currents, &c, proceeds to a comparison of results. Taking 

 the list of 36 localities of which Professor Everett gives the recorded 

 results, and classifying them as — 1. Metallic Mines ; 2. Coal Mines ; 

 3. Wells and Wet Borings ; 4 Tunnels ; he found that in the — 



Metallic Mines, the increase of temperature with depth varied from 



1° F. in 47 feet to 1° in 126 feet ; 

 Coal mines, the range was 1° F. in 45 feet to 1° in 79 feet ; 

 Wells and borings gave from 1° F. in 41 feet to 1° in 130 feet, or 



excluding the wells of La Chapelle and Bootle, which are open to 



suspicion of convection currents, the least rate of increase was 1° 



in 69 feet ; 



Tunnels. In the only two great tunnels in which observations have 

 been made, that of Mont Cenis gave an increase of 1° for 79 feet, 

 and that of St. Grothard of 1° for 84 feet, but in a subsequent report 

 Dr. Stapff has shown that an important modification is necessary 

 for a portion of the tunnel. 



In deducing a mean from these various results, Professor Everett has 

 considered it best to operate not upon the number of feet per degree, 

 but upon its reciprocal — the increase of temperature per foot ; and 

 assigning to the results of the observations at the thirty-six localities 

 of which he gives the list, weights proportional to the depths, he finds 

 the mean increase of temperature per foot to be 0'1563, or about 

 of a degree per foot — that is, 1° F. in 64 feet.* In the subsequent 

 report of 1883, however, taking the corrected readings of Stapff for 

 the St. Gothard and Mont Cenis tunnels, this mean is reduced to 1° F. 

 in 60 feet. 



Scattered observations have also been made within the last few 

 years in different parts of the world, some in particular of much 

 interest on the deep hot artesian well of Buda-Pestb, by Professor 

 Szabo, and by others in America and elsewhere ; while temperatures 

 of a number of ordinary wells have been taken by the Rivers Pollution 

 Commission. Amongst those to whom I am indebted for furnishing 

 me with observations in wells and mines in their respective districts, 



* Professor Everett observes, however, in a previous paper (1874) that some of 

 the best observations give a rate of about 1° F. for 56 feet of descent, and that this 

 seems a fair average. 



