INTERNAL HEAT OF THE EARTH. 39 



of the sea ; the waters, consequently, rise to a total height of 

 580*33 metres, or 1904 feet. The temperature of the spring 

 is 81°*95 P. ; consequently the increase of heat marks 1° F. 

 for about every 59 feet. 



The borino; at the New Salt-works at Ilchmc is situated 

 231 feet above the level of the sea (above the water-mark at 

 Amsterdam). It has penetrated to an absolute depth of 

 2281 feet below the surface of the earth, measuring from the 

 point where the operations were begun. The salt spring, 

 which, when it bursts forth, is impregnated with a large 

 quantity of carbonic acid, lies, therefore, 2052 feet below the 

 level of the sea — a relative depth which is perhaps the great- 

 est that has ever been reached by man in the interior of the 

 earth. The temperature of the salt spring at the New Salt- 

 works of Oeynhausen is 91° 04 F. ; and, as the mean annual 

 temperature of the air at these works is about 49°-3 F., we 

 may assume that there is an increase of temperature of 1° F. 

 for every 54-68 feet. The boring at these Salt-works* is, 

 therefore, 491 feet absolutely deeper than the boring at Gre- 

 nelle ; it sinks 377 feet deeper below the surface of the sea, 

 and the temperature of its waters is 9°*18 F. higher. The 

 increase of the heat at Paris is about 1° F. for 59 feet, and 

 therefore scarcely -^th greater. I have already elsewhere 

 drawn attention to the fact that a similar result was obtained 

 by Auguste de la Rive and Marcet, at Bregny, near Geneva, 

 in investigating a boring which was only 725 feet in depth, 

 although it was situated at an elevation of more than 1G00 

 feet above the Mediterranean Sea.f 



If to these three springs, which possess an absolute depth 

 varying between 725 feet and 2285 feet, we add another, 

 that of Monkwearmouth, near Newcastle (the water rising 

 through a coal-mine which, according to Phillips, is worked 



* According to the manuscript results given by the superintendent 

 of the mines of Oeynhausen. See Cosmos, vol. i., p. 157, 174; and 

 Bischof, Lehrbuch der Ghem. unci Phys. Geologie, bd. i., abth. 1, s. 154- 

 1G3. In regard to absolute depth the borings at Mondorf, in the 

 Grand Duchy at Luxemburg (2202 feet), approach most nearly to those 

 at the New Salt-works at Oeynhausen. 



f Cosmos, vol. i., p. 174 ; and Mcmoires de la Societe d'llist. Naturelle 

 de Geneve, t. vi., 1833, p. 243. The comparison of a number of Arte- 

 sian wells in the neighborhood of Lille with those of Saint Oucn and 

 Geneva would, indeed, lead us to assume, if we were quite certain as 

 to the accuracy of the numerical data, that the different conductive 

 powers of terrestrial and rocky strata exert a more considerable in- 

 fluence than has generally been supposed (Poisson, Thcorie Mathema- 

 tique de la Chaleur, p. 421). 



