610 



Fourier s Theory of Heat. 



to the planetary spaces, independent of the primitive heat which the 

 globe has preserved. 



" In order to acquire the knowledge of this singular phenomenon, 

 it is requisite to examine what would be the thermometrical state of 

 the terrestrial mass, if it received heat only from the sun ; and in 

 order to make this examination easier, we will first suppose the 

 atmosphere to be destroyed. Now, if no cause exists adapted to 

 give a common and constant temperature to the planetary spaces — 

 that is to say, if the terrestrial globe, and all the bodies which com- 

 pose the solar system, were placed in an enclosure devoid of all heat, 

 phenomena would be observed entirely contrary to those which we 

 know to exist. The polar regions would endure an immeasurable 

 cold, and the decrease in the temperature, from the equator to the 

 poles would be incomparably more rapid and extensive. 



" Upon the hypothesis of the absolute cold of space, if it is possi- 

 ble to conceive it at all, the effects of heat, such as we observe them 

 on the surface of the globe, would be owing to the presence of the 

 sun ; the least variations of distance from that orb, would occasion 

 very considerable changes of temperature in the earth; the inter- 

 mission of days and nights would produce sudden and totally different 

 effects from those which we perceive. The surface of bodies would 

 instantaneously be exposed, at the commencement of night, to an in- 

 finitely intense cold ; and animated bodies and vegetables would not 

 be able to resist the equally strong and sudden action of a contrary 

 description, which would take place upon the rising of the sun. 



" The primitive heat preserve in the interior of the terrestrial 

 mass, would not maintain the exterior temperature of space, nor pre- 

 vent any of those effects which we have just described ; for we know 

 with certainty (as we have just seen) by theory and observation, that 

 the effect of this central heat has long since become imperceptible at 

 the superficies, although it may be very great at a middling depth. 



" We conclude from these last remarks, and principally from the 

 mathematical examination of the question, that there exists a physi- 

 cal cause always present, which moderates the temperatures at the 

 surface of the terrestrial globe, and gives to this planet a fundamen- 

 tal heat, independent of the action of the sun, and its own heat which 

 the interior mass has preserved. This fixed temperature, which the 



