4 



Prof. J. Prestwich. 



At this time a number of deep artesian wells were being made in 

 France by Messrs. Degousee and Laurent and other engineers, and 

 M. Walferdin invented an overflow maximum thermometer, which 

 carefully guarded against pressure, gave excellent results, and which 

 he employed to check many of the earlier observations made without 

 this necessary precaution. The numerous artesian wells also made 

 about this time in Algeria, Venice, and other parts of the Continent 

 by Degousee and Laurent, gave important results. Those in Algeria 

 seem to show that the rate of increase is there more rapid than in 

 Europe. 



Admirable discussions of the question were made from time to time 

 by Arago : the last being that published in his " OEuvres Complets " 

 in 1856. In this he reviews the whole subject, gives elaborate par- 

 tic nlars of most of the recorded observations, with the advantage of 

 more accurate surface temperatures, and concludes that the rate of 

 increase is very variable, and may be taken at from 20 to 30 metres 

 for each degree centigrade. 



In 1861 Sir W. Fairbairn gave an account of the observations, so 

 frequently referred to, in the Dukinfield Colliery, where the rate of 

 increase was estimated at 1° F. for every 79 feet. 



Professor Hull also brought together in his " Coal Fields of Great 

 Britain" (Edit. 1873), a number of observations made in the coal- 

 pits of this country, and drew especial notice to the Rosebridge 

 Colliery temperatures. The general conclusion at which he arrived 

 was that the underground temperature varies, being much influenced 

 by the dip of the strata, but may, as a mean, be taken at 60 feet per 1°. 



The Royal Coal Commission of 1866-70 was the means of obtaining 

 through its Committee " On the Possible Depth of Working," a mass 

 of most valuable evidence from practical coal-owners, inspectors, and 

 managers, relating to the temperatures at depths in the coal mines of 

 Great Britain. The general opinion of these gentlemen was that the 

 temperature increased at the rate of about 60 to 63 feet for each 

 degree F., and the Committee concluded that the rate of increase 

 of the temperature of the strata in the coal districts of England is in 

 general about 1° F. for every 60 feet of depth. 



In 1867 a Committee of the British Association was appointed (at 

 the suggestion, I believe; of Sir W. Thomson) " for the purpose of in- 

 vestigating the Increase of Underground Temperatures downwards in 

 various Localities of Dry Land and under Water," with Professor 

 Everett as secretary. To this Committee we are indebted for a series 

 of sixteen very valuable annual reports, in which are recorded a large 

 number of observations carried on with corrected instruments supplied 

 by the Committee, and under the able superintendence of its secretary. 

 Each set of observations is discussed at length ; the causes of inter- 

 ference are considered ; and detailed particulars are given of all the 



