28 REMARKS OX TEMPKRATURE OF THE EARTH IX MIXES. 



illustration from facts ; the assertion therefore, that the incre- 

 ment of temperature corresponds on the average to about 1 deg- 

 Fahrenheit for every 7 fathoms of descent rests rather on theory 

 than experience." Atkinson on explosives in coal mines says. — 

 " The temperature of the earths crust increases with its depth; 

 at 50 feet from its surface the temperature is 50 degs. Fahrenheit, 

 and below that depth the temperature rises 1 deg. for every 60 

 feet." No proof is given, and the statement is evidently of local 

 reference and respecting coal mines. The Royal Commission on 

 Coal in 1870 appeared to think that it would be possible so to 

 cool a mine that operations might be carried on at a depth of 

 GOOO feet. And if a coal mine, surely a metalliferous mine with 

 much less difficulty. 



The theory appears to have been formed at a comparatively 

 early period in the history of mining, and as it is a subject in 

 which few mining managers take much interest, it has been 

 accepted rather than proved. Nearly all those who discuss the 

 subject are scientific men who take the recorded observations of 

 others, without any reference to the conditions under which they 

 were taken, although it is evident that in many cases the avoid- 

 able causes of heat would go far to account for the recorded in- 

 crease of temperature ; but no one appears to have questioned or 

 combatted the correctness of the theory by opposing evidence,, 

 although it would be difficult to find any other scientific theory 

 based on facts so questionable and so utterly at variance with 

 each other. 



Hunt, Mungo Ponton, Ansted, Richardson, Geikie, Lyell, 

 Chambers' Encyclopedia, the Globe, Encyclopa'dia Britannica, 

 and a host of other writers and works have been consulted, but 

 nothing further has been found than a repetition of the assump- 

 tion already mentioned, with an occasional doubt or query, but 

 the most noticeable fact is the great discrepancy between the con- 

 clusions arrived at even by the deepest thinkers on the subject. 

 Phillips, says Mr. Hodgkinson, at the request of the British 

 Association, made some experiments in the comparatively shallow 

 salt mines of Cheshire which gave an augmentation of 1 deg. 

 for every 70 feet from the surface. Observations by Buddie, 

 Bald, Peace, Hodgkinson, and others in coal mines are also 



