6 Prof. J. Prestwich. 



not hitherto recorded, are Professor Gr. Dewalque of Liege, Professor 

 Gosselet of Lille, M. F. L. Cornet of Mons, and others. 



Professor Lebonr has further discussed the subject, with reference 

 especially to the nature of the experiments still required to improve 

 our knowledge of it, in an interesting paper read before the North of 

 England Institute of Mining and Mechanical Engineers, in 1882. In 

 this he gives a list of observations made at fifty-seven localities, and 

 deduces from them an average rate of increase of 1° F. per 64*28 feet 

 of descent ; but he remarks that all the observations recorded are by 

 no means of equal value, and points out that the mean rates of increase 

 in the best observations cluster about the numbers 1° F. per 50 or 

 60 feet. 



General List. (Table I, p. 56.) 



I have given in a general list all the observations on underground 

 temperatures of which I have been able to find a record.* The 

 number of different localities, mines, &c, where such observations 

 have been recorded, amounts to 248, and the number of stationsf to 

 530. I have only omitted a few which were obviously wrong, together 

 with some of the observations repeated frequently in the same mine, 

 or repeated more frequently thau necessary for our object in mines in 

 the same district, and which would only add needlessly to the length 

 of the list. J Neither have I considered it necessary to give in all 

 cases the full details of the observations, as these will be found in the 

 original papers referred to. I have confined myself to giving the 

 principal and essential facts and results. 



The observations are given in the order of date, an order which, as 

 a general rule, agrees with that of their reliability, although there are 

 several remarkable exceptions. The superiority of the later observa- 

 tions consists chiefly in the perfection of the instruments and methods 

 of experimentation. Most of the more general disturbing causes 

 interfering with accuracy of the results were well understood and 

 guarded against by the early observers. 



The particulars of depth, temperature, and modes of proceeding, 

 are given in the terms of the original observers. On two points only, 

 on which their information was often unavoidably imperfect, have I 

 made any alteration — points which even now are in many cases not 

 accurately determined — viz., the mean annual temperature of the 

 surface, and the height of the surface above the sea-level. These 



* I should feel greatly obliged by information respecting any other observations. 



f By " station " I mean all tbe separate points in a mine, or at the several depths 

 in a well, at which the observations have been made. 



X Mr. Henwood's long and valuable series of observations in the Cornish and 

 foreign mines will be found in vols, v and viii, " Trans. Roy. G-eol. Soc, Cornwall." 

 I have given all his principal instances. 



