1886.] NEW YORK ACADEMY OF SCIENCES. 21 



scenes of violent volcanic action. The surface of the country 

 is occupied by vast sheets of lava, hot springs abound there, and 

 it is evident that the subterranean fires are not yet extinguished. 

 A boring on the flanks of Mt. Etna would be a still more strik- 

 ing exception to the rule of one degree for every 50 feet, and 

 would be equally legitimate evidence against it. 



Excluding these abnormal cases, which really have no bearing 

 on the question, tlie irregularities in the rate of increase in tem- 

 perature are not greater than those which miglit be caused by 

 differences in the conductivity of the rocks passed through. The 

 deep wells of Sperenberg and Schladenbach — which were bored 

 in part to test this question, and have been the most carefully 

 observed of any — have given the most convincing evidence of 

 the truth of the tiieory of intense internal heat.* The case 

 cited bv Professor Judd {Volcanoes, p. 341), "a deep well in 

 Buda-Pesth, in which there was a decline of temperature below 

 3,000 feet," is probably a mistake or a fraud. The same thing 

 happened at the deep well at St. Louis, in which the tempera- 

 ture increased regularly to the depth of 3,200 feet, where it was 

 107° Fahr. Below that the contractor reported the temperature 

 declining, because the directors were about to stop the tvork, partly 

 on account of the warmth of tlie loater I To prevent exposure of 

 the fraud, iron rails were dropped into the well. 



It may then be considered as established that all over the 

 earth's surface, except in volcanic districts, the temperature in- 

 creases about one degree Fahr. for every 50 feet descent. It is 

 evident tliat should this rate of increase continue, the tempera- 

 ture at the depth of 50 miles would be sufficient to melt all 

 known substances; and the first conclusion from the observation 

 of temperature in mines and wells was that the solid portion or 

 crust of the earth could not be more than 40 or 50 miles in 

 thickness, and it was proclaimed that we were living on a film 

 of solid matter, floating on a sea of molten rock. The com- 

 parative stability, however, of the earth's figure — the little 



