16 On the Progressive Increase of Temperature 



comes stationary at about 36° Fah. varies from two hundred to five 

 hundred fathoms. Below this there is probably no change of tempe- 

 rature. M. Lenz found it to sink no lower as far down as one thou- 

 sand fathoms ; but we can expect no increase of temperature without 

 a complete subversion of the law of nature, by which a maximum 

 of density is imparted to water. 



It would appear, then, that the evidence at present is decidedly in 

 favor of a great central heat in the globe, even leaving out of consid- 

 eration the easy explanation it affords of so many geological phenom- 

 ena. But a new source of evidence has lately been opened, and one 

 much less liable to objections than the high temperature of mines, — 

 in the borings for water lately practised to such an extent in France 

 and Germany. 



It was an important observation of Mr. Fox, that the water which 

 gushed out from springs at the bottom of the Cornish mines had al- 

 ready the temperature of the air in the places where it appeared, and 

 was completely convincing as to the source of the heat so long observ- 

 ed. The Artesian springs of the continent confirm his observation. 

 In general, the water which flows from them is of a higher tempera- 

 ture than the mean of the earth at the place, and is warmer as its 

 source is deeper. At Vienna forty or fifty have been formed, and 

 the water of all has a temperature varying from 52° to 58°, the 

 mean temperature, according to Humboldt, being 50.54° F. At 

 Heilbronn in Wurtemberg, five borings sunk to supply a paper mill 

 to the depth of from sixty to one hundred and twelve feet, deliver 

 water having a temperature of about 55° ; and the proprietor has 

 taken advantage of it to warm his works in the winter, and succeed- 

 ed in keeping the apartments at a temperature of 46° when that of 

 the air was 25° below zero of Fah. 



There are, however, many exceptions and anomalies which are 

 not to be wondered at, when we consider, that, from the inclination 

 of the strata and other causes, the depth of the boring is no sure in- 

 dication of the true level from which the water comes. It is only 

 when we are sure beforehand of the nature of the strata, that we can 

 come to correct conclusions in regard to the true temperature of the 

 earth at any given depth. 



One of the most interesting of the exceptions we have met with, 

 and which illustrates best the nature of the anomalies we may expect 

 to meet with, is the case of a tube of three inches and a quarter in 

 diameter, sunk to the depth of three hundred and thirty five feet at 



