THE SUBTERRANEAN FURNACE 341 



"What you have just told us, Uncle," said Jules, 

 "shows plainly that there is great heat under 

 ground." 



"In admitting, as all these observations justify us 

 in doing, that the subterranean temperature in- 

 ises with the depth one degree for every thirty 

 m.'U'rs, it is estimated that at three kilometers or 

 tlnve quarters of a league down, the temperature 

 must be that of boiling water, that is to say 100 

 degrees. Five leagues down, the heat is that of 

 red-hot iron; at twelve leagues it is sufficient to 

 melt all known substances. At a greater depth the 

 temperature, apparently, is still higher. Accord- 

 ingly we are to imagine the earth is formed of a 

 globe of matter liquefied by fire and enveloped by 

 a thin crust of solid material that is upborne by 

 that central ocean of melted minerals." 



"You say," said Claire, "a thin crust of solid 

 material; and yet, according to the calculations you 

 have just mentioned, the thickness of the solid ma- 

 terial must be about twelve leagues. Under that 

 would be the melted matter. It seems to me twelve 

 leagues make a good thickness, and we have noth- 

 to fear from the subterranean fire." 



"Twelve leagues are very little in relation to the 

 <;irth's dimensions. The distance from the surface 

 of the earth to its center is 1600 leagues. Of this 

 distance about twelve leagues belong to the thick- 

 ness of the solid crust, all the rest to the molten globe. 

 On a ball two meters in diameter the solid crust 

 of the earth would 1> ivprrsrnt.'d by a thickness of 

 half a finger's breadth. Let us make a more simple 



