The Evolution of the Sciences 



a quantity of heat which may be estimated 

 roughly at one calorie ' per square metre per 

 minute. The sun, on a fine summer day, sheds 

 on the same surface in the same space of time a 

 calorific energy twenty thousand times greater. 

 Thus the contribution of the central heat is insen- 

 sible to us, chiefly owing to its extreme feeble- 

 ness and partly because it is constant; we are 

 affected only by variations of temperature. 

 These figures enable us, notwithstanding their 

 indifferent accuracy, to estimate in passing the 

 value of an idea which finds frequent expression, 

 viz., Why not take the necessary heat for supply- 

 ing our industrial requirements from the furnace 

 beneath our feet? 2 



1 Calorie is the quantity of heat required to raise the 

 temperature of one gramme of water one degree C. 



2 We may recall the words pronounced by M. Berthelot 

 (Science et Morale, p. 508) in a most humorous description 

 of the state of the world in the year 2000: "To tap the 

 central heat, all that is needed are shafts sunk to a depth of 

 four or five thousand metres, a task probably within the power 

 of living engineers, and still more of those of the future. 

 There would be found heat, the origin of all life and all 

 industries. At the bottom of these shafts water would reach 

 a high temperature, and would develop sufficient pressure to 

 drive all possible engines. Power would therefore be available 

 at all points of the globe, and thousands of centuries would 



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