346 Prof. BischofF on the Temperature of 



Thus we find that the maxima and minima take place at an 

 earlier period than that given by the thermometrical observa- 

 tions made at greater depths in mines, which is in perfect ac- 

 cordance with the theory. We see further, that the differences 

 between maximum and minimum deci-ease with the depth, and, 

 indeed, much more rapidly than in the Saxon mines. This cir- 

 cumstance again proves that the temperature of the air lias a 

 considerable influence on observations in mines, and that a con- 

 stant temperature would be found at a much lesser depth, if the 

 thermometers could be constructed of much greater length than 

 four feet, and the temperature of the earth be thus observed at 

 a greater depth. 



It is very remarkable that the observations made at Abbots- 

 hall and Brussels should give such a considerable increase of 

 mean temperature at depths differing but by a few feet. As the 

 observations at Stockholm shew but a scarcely perceptible in- 

 crease of temperature, and as they were made with the greatest 

 care, it is highly probable that at the other places the observa- 

 tions were influenced by accidental circumstances. 



Chap. IX.— Caw it be maintained with certainty that the glaciers are 

 melted from underneath by the internal heat of the earth, and tvhat 

 thermometrical phenomena accompany glaciers in general? 



The phenomena under consideration has already been pointed 

 out by De Luc,* De Saussure,+ and others, who have endea- 

 voured to account for it by the continual radiation of the inter- 

 nal heat of the earth. Escher, j: who observed the glaciers with 

 great caution, considers this melting of the glaciers from under- 

 neath as an undeniable fact. He says, " They would soon reach 

 the highest limits of the mountains between which they are con- 

 tained, were they not melted away from underneath by the in- 

 ternal heat of the earth, so as to cause the underminings and 

 fallings in, by which an equilibrium is constantly maintained in 

 the mass of the glaciers, between the accumulations at the sur- 

 face and the loss sustained from underneath. It is by this 



':.-ifl7/ r-i. 

 • Rech. sur I'Atmosph. ii. 327. t Voyages dans les Ali)es, § S33. 



4; Gilbert's Annalen, Ixix. p. 113. 



