May 26, 1911] 



SCIENCE 



829 



tions, that the earlier observations were in- 

 ferior and of little value for purposes of accu- 

 racy, due chiefly, he says, to the imperfection 

 of instruments and methods of experimenta- 

 tion. Because of the careful digest by Pro- 

 fessor Prestwich of the voluminous data bear- 

 ing on this subject, I regard it of sufficient 

 interest to note briefly the following extracts 

 from this valuable paper. The author classi- 

 fied the recorded results on underground tem- 

 peratures into — (1) metallic mines, (2) coal 

 mines, (3) wells and wet borings and (4) tun- 

 nels. The increase of temperature was found 

 to be: (1) metallic mines, from 1° F. in 47 

 feet to 1° F. in 126 feet; (2) coal mines, from 

 1° F. in 45 feet to 1° F. in 79 feet; (3) wells 

 and borings, from 1° F. in 41 feet to 1° F. in 

 130 feet; (4) tunnels— Mont Cenis, 1° F. for 

 79 feet; St. Gothard, 1° F. for 84 feet. The 

 mean of these results gave 1° F. in 64 feet. 

 Subsequent corrected readings in the two tun- 

 nels reduced the mean to 1° F. in 60 feet. 



Professor Prestwich regarded the differences 

 in resTilts obtained in mines, wells, etc., indi- 

 cated by an examination of the tables, to be 

 attributed to the fact that the geological con- 

 ditions were unlike, and the disturbing causes 

 of a different order. The main disturbing 

 causes in the different groups of openings 

 made are stated and discussed. In coal mines 

 they are stated as (1) loss of heat through 

 exposed surfaces, (2) effects of ventilation, 

 (3) other causes, such as crushing of rock, 

 escape of gas, and effects of irregularities of 

 surface (pp. 9-21). There are local varia- 

 tions according to structure, percolation of 

 water, etc. From the reliable cases, the mean 

 increase for coal mines was found to be 1° F. 

 in 50 feet. 



In metalliferous mines the main causes af- 

 fecting thermal conditions are given as (1) 

 ventilation, (2) percolation of water, (3) hot 

 springs, due (a) to chemical decomposition 

 and (b) to water coming from great depths' 



' In his revised paper, Professor Prestwich adds 

 "the working operations" to the list of causes 

 affecting thermal conditions in metalliferous 

 mines. "Collected Papers on some Controverted 

 Questions of Geology," 1895, p. 179. 



(pp. 25-34). The mean thermometric gradi- 

 ent was found to be 1° F. in 44 feet in rock, 

 and 1° F. in 42.4 feet in springs, with an 

 average for the two of 1° F. in 43.2 feet. 



In wells and borings the main disturbing 

 causes are regarded as (1) pressure on the 

 instruments, and (2) convection currents. The 

 mean thermometric gradient in this group of 

 openings was found to be for non-flowing 

 wells 1° F. in 51.2° feet, in flowing wells 1° F. 

 in 49.1° feet, with an average for the two of 

 1° F. in 50° feet. 



A paper entitled " Eock Temperatures on 

 the Rand and Elsewhere," by E. M. Weston," 

 published in a recent number of the South 

 African Mining Journal is of interest. The 

 tables which follow below are taken from this 

 paper. 



MocTc Temperatures in Depth on Witwatersrand 

 Mines 



Rock Tem- 

 perature at 



1,000 feet 68.75° F. 



2,000 feet 73.53 



3,000 feet 78.35 



4,000 feet 83.15 



5,000 feet 87.95 



6,000 feet 92.75 



7,000 feet 97.55 



8,000 feet 102.35 



General rate of increase, 1° F. for 250 feet. 



In the Lake Superior copper district, the 

 Tamarack shaft is reported to have reached a 

 depth of 6,070 feet, and the Red Jacket shaft 

 a depth of 5,315 feet. The rate of increase in 

 temperature is given as 1° F. for 209 feet. 

 In a note published by Professor Alexander 

 Agassiz in 1895, the greatest depth reached in 

 the Calumet shaft was 4,712 feet, which 

 showed an average increase in temperature of 

 1° F. for 223.7 feet." Two bore holes are re- 

 ported put down in Silesia to depths of 6,500 



" 52.2, 50.6 and 51.4 feet, respectively, in the 

 revised paper. Itid., 1895, pp. 228 and 231. 



" South African Mining Journal, November 1 2, 

 1910, p. 417. 



" ' ' On Underground Temperatures at Great 

 Depths," Am. Jour. Sci., 1895, Vol. L., pp. 503- 

 504. 



