I00 The Interior of the Earth. [Sess, 



increase of 1° for every 58 feet of depth. Another well near 

 Paris, at La Chapelle, where observations were taken at dif- 

 ferent depths, gave the following results: — 



Depth. Temperature. 



330 feet 59|° Fahr. 



660 ,. 62 ° o " 



1000 „...•• 65|° ii 



2200 „. . • • . 76° i. 



These figures give a slower rate of increase — viz., only 1° F. 

 for every 82 feet. 



At Sperenberg, near Berlin, a boring was made to a depth 

 of 4172 feet, nearly all through rock-salt, and the temperature 

 observed at a depth of 4042 feet, when corrected for pressure, 

 gave a result of 1° F. for every 51| feet. 



In considering the evidence afforded by geysers and hot 

 springs as to internal heat, those which occur in the neighbour- 

 hood of volcanic centres must be regarded as deriving their 

 heat from proximity to the locally heated rocks, which of 

 course may not be at any great depth. 



Warm springs at a distance from volcanoes, such as those 

 of Bath or Buxton, appear to rise through fissures of great depth 

 in the crust, and may owe their comparatively high tempera- 

 ture merely to the distance underground of their origin ; and 

 they must probably lose a considerable portion of their initial 

 heat by parting with it to the rocks they traverse on their way 

 to the surface. 



From all the foregoing considerations it is plain that the 

 farther we pierce into the crust of the earth the hotter it 

 becomes ; and, starting with this fact, we are more in a posi- 

 tion to consider, by inference, the probable condition of the 

 earth at very great depths, and this brings us to the second 

 head in our inquiry. To solve the problem now before us the 

 aid of mathematics has been largely employed, based on de- 

 ductions from physical experiments, and also from astronomical 

 observations. The value of such inferences in an undertaking 

 of this nature is largely discounted by our total want of know- 

 ledge of the behaviour of matter under the influence of the 

 enormous pressure to which it must be subjected in deep- 

 seated regions of the earth. 



