1859.] Mr, Hopkim on the EariKs Temperature, 139 



WEEKLY EVENING MEETING, 



Friday, May 13, 1859. 



Sir Henry Holland, Bart. M.D. F.R.S. Vice-President, 

 in the Chair. 



William Hopkins, Esq. M.A. LL.D. F.R.S. 



On the EartKs Internal Temperature^ and the Thickness of its 

 Solid Crust, 



If we descend beneath the surface of the earth, and observe the 

 temperature at different depths, it is found that within a depth ranging 

 from 50 to 80 feet, the temperature changes periodically, being affected 

 to that depth by the heat which the earth receives from the sun at 

 different seasons of the year. The annual variation, however, becomes 

 less as the depth increases, till at the depth above mentioned it becomes 

 insensible. At greater depths, the temperature is invariable at each 

 point, but increases with the depth, at the rate, on an average, of 1° (F.), 

 for a depth of between 60 and 70 feet. The best observations which 

 have been made on this subject are those in deep mining shafts and 

 deep artesian wells; the greater the depth the more completely do 

 anomalous influences counterbalance each other. The greatest depths 

 at which such observations have been made in Western Europe, are at 

 Monkwearmouth and Dukinfield in this country ; the Puits de 

 Grenelle, at Paris ; MondorlF, in the Duchy of Luxembourg ; New 

 Seltzwerk, in Westphalia ; and at Geneva. At the first two places the 

 observations were made in vertical shafts of coal mines ; the depth of 

 the one at Monkwearmouth being upwards of 1800 feet, and that at 

 Dukinfield upwards of 2000 feet; and in both cases the observa- 

 tions were made while the workmen were sinking the shafts, and with 

 every precaution against the influence of any extraneous causes which 

 might affect the observations. The former gave an increase of 1° (F.) 

 for every 60 feet of depth, the latter for about every 72 or 73 feet. 

 The sinking of the Puits de Grenelle was superintended by Arago. 

 The mean increase of temperature was l** for every 60 feet At 

 Mondorff the bore was 2400, being that of an artesian well ; the 

 increase was P for 57 feet. At New Seltzwerk the artesian well, 

 penetrating to the depth of 2100 feet, giving an increase of P (F.) for 

 55 feet. The average of these is very nearly 1** for 60 feet. Nume- 

 rous other observations are confirmatory of those results, though obser- 

 vations at smaller depths present many anomalies indicating the 

 operation of local causes. 



