LAMBERT: CONSTITUTION OF THE EARTH 1 23 



The view that the interior is hot and fluid is certainly not 

 wholly unsound. First, as to the heat. As far down as borings 

 have been made into the earth, the temperature increases with 

 the depth ; the rate is very variable from place to place ; i ° C . 

 for each 35 meters may perhaps be taken as a fair mean, or in 

 ordinary units say i ° F. for each 60 feet. The discovery of 

 radium and of the great quantity of heat given out by even a 

 minute quantity of it suggests the possibility that the heat sup- 

 plied by radium may exceed the heat radiated into space 

 so that the earth may be gaining instead of losing heat.- What 

 the temperature of the interior is we cannot say. If the rate of 

 increase of i ° C. for each 35 meters should hold good clear to the 

 center, the temperature there would be 180,000° C. Such a 

 temperature does not agree with present ideas. Men of science 

 do not talk of a solar temperature of millions of degrees, as did 

 their predecessors of a generation or two ago. They are content 

 to accept a solar temperature of a few thousand degrees, and our 

 estimates of terrestrial temperatures must be correspondingly 

 lowered. It is almost certain, however, that the temperature is 

 high enough to melt rock under the surface conditions of pressure, 

 but the increased pressure may raise the melting point so much 

 that no actual liquefaction occurs. Volcanoes are supposed to 

 be isolated "pockets" of molten matter unconnected with any 

 central reservoir. 



As far as the fluidity is concerned, if the earth be not fluid, it 

 acts in some ways as if it were. It seems improbable that a gravi- 

 tating body the size of the earth and composed of any species of 

 matter with which we are acquainted should sufflciently resist 

 as a whole the long-continued action of the stresses that would 

 arise from any great departure from the conditions of fluid 

 equilibrium. The flow of rock may resemble that of ice in a 

 glacier, which is a process of rupture followed by reunion under 

 pressure. The theory of fluidity, at all events, has served us 



- The phrase "gaining heat" is used advisedly instead of "rising in temperature." 

 For a body sufficiently large, a rise in temperature would accompany a loss of heat, 

 owing to the gravitational work done in contracting. It is possible that the earth 

 is large enough for this to be the case, so that a loss of heat would accompany a rise 

 in temperature and vice versa. See Rudzki, Physik der Erde, p. ii8. 



