of the Terrestrial Globe. 207 



been their mutual ire, have contended with arguments but little 

 decisive, taken from the phenomena of geology ; but which have 

 left the rigid inquirer in suspense. The true mode of termina- 

 ting this debate, evidently was to examine if there existed in the 

 interior of the earth, any circumstances which gave certain signs 

 of the original heat invoked by the Plutonists. To this import- 

 ant problem, naturalists and geometricians have succeeded, by 

 united efforts, in finding a satisfactory solution. 



In every part of the globe, on descending to a certain depth, the 

 thermometer ceases to exhibit either a diurnal or an annual varia- 

 tion. It invariably indicates the same degree, and the same frac- 

 tion of a degree, during all the year, and during a succession of 

 years. Such is the fact; and now, what is the theory ? Let us sup- 

 pose for a moment that the earth had received all its heal from the 

 sun, then the calculation, on this hypothesis, would teach us, 

 1st, that at a certain depth the temperature would be invariable ; 

 and, 2d, that this solar temperature of the interior of the globe 

 would change with the latitude. On these two points theory and 

 observation agree. But, according to this theory, it must more- 

 over be added, that in each climate, the invariable temperature 

 of the strata should be the same at all depths, so long at least, 

 as we do not descend to a very great extent, relatively to the 

 earth's diameter. But every one knows that this is not the case. 

 Observations made in a vast multitude of mines, and others made 

 on the temperature of the water issuing from a great number of 

 springs at different depths, agree in giving an increase of nearly 

 2° Fahr. for every sixty or ninety feet of descent. When a hy- 

 pothesis leads to a result so completely in opposition to the facts, 

 it is false, and ought unhesitatingly to be rejected. Thus, it is 

 contrary to the truth, that the phenomena of the temperature of 

 the successive strata of the earth, can be attributed to the sole ac- 

 tion of the solar rays. 



The solar action being thus rejected, the cause of the regular 

 increase of caloric, observed universally, as we penetrate into 

 the interior of the globe, can only be referred to an original heat 

 belonging to the earth itself. The earth, as the Plutonists will 

 have it, and Descartes and Leibnitz before them, the one as 

 well as the others, — the earth, it must needs be, avowed, even 

 without any demonstrative proof, is now become expressly, an 



r 2 



