44 C. R. VAN HISE 



sider the random hot springs. If these were the basis of calcu- 

 lation it would indeed be unimportant. But if underground 

 waters upon the average reach the surface with a slightly higher 

 temperature than when they entered it, this may be a very impor- 

 tant means by which heat is lost through convection. While 

 difficult or impossible to prove by observation, I think it is 

 unquestionable that underground waters must escape at a tem- 

 perature upon the average somewhat higher than that with which 

 they entered the earth. The average temperature of water when 

 it enters the land may be presumably taken as that of the average 

 of the surface of the earth at that locality. From this average 

 temperature at the surface the temperature of the rocks increases 

 downward. The vast quantities of water which at all times is 

 taking an underground journey gains heat as a result of its 

 contact with the warmer rocks. At another time I shall attempt 

 to show that the water thus heated finally reaches the surface 

 without losing all of the heat gained in its downward course. 

 If this be so, there is constant loss of heat. 



So far as I know, no attempt has ever been made to estimate 

 the heat lost to the earth by means of the convectional under- 

 ground currents of magma and water. While I am wholly unable 

 to prove it, I have no doubt that the absolute quantity of such 

 heat is enormous. The heat transferred by convection is to be 

 added to the amount transferred by conduction. 



As having an effect opposite to that of conduction and con- 

 vection in lowering the average temperature of the earth, it is 

 to be noted that as a result of changing rotation period (con- 

 sidered pp. 54-59) heat develops within the earth in two ways. 

 First, heat is developed by tidal friction. Darwin states that he 

 has " calculated that the heat generated in the interior of the 

 earth in the course of the lengthening of the day from 5 hours 

 36 minutes to 23 hours 56 minutes would be sufficient, if applied 

 all at once, to heat the whole earth's mass about 3000 F., 

 supposing the earth to have the specific heat of iron." x Second, 



1 On the precession of a viscous spheroid, and on the remote history of the earth, 

 by G. H. Darwin : Phil. Trans. Roy. Soc, Vol. CLXX, Ft. II, 1879, p. 535. 



