DEPTH OF PERPETUAL BOILING. Gl 



at a depth of twenty thousand feet below the 

 surface of the earth — has an elasticity fifteen times 

 as great, although its heat is only doubled. At 

 a temperature of 265° C. (509° P.) steam has an 

 elasticity equal to fifty atmospheres ; that is, it 

 could sustain the pressure of a water-column 

 seventeen hundred feet high. We have no accu- 

 rate experiments beyond tins ; but this is enough 

 to show us that at some depth below the surface of 

 the earth the efforts of the water to throw off 

 vapour must reach the strength necessary to heave 

 up the liquid column that presses upon it, whatever 

 may be the height of that column. At this depth 

 therefore the water must be always kept by the 

 heat of the earth in a boiling state, and therefore 

 must fill any hollows it may find at hand with 

 water in a gaseous state. Calculation, winch how- 

 ever by reason of the imperfect data on which it 

 is founded, cannot claim any greater value than 

 that of approximation, places this point for the 

 middle of Europe at a depth of about forty thou- 

 sand feet, and the corresponding temperature of 

 the water at 414° C. (777° F.) All water that 

 might get down lower than this would be the 

 more certainly turned into steam. 



The vapour thus formed rises up in the channels, 

 clefts and hollows, through which the water had 

 run down. But in the higher regions it does not 

 iind the temperature which it requires to enable it 



