Fourier s Theory of Heat. 



611 



earth thus receives from space, differs little from that which would be 

 indicated at the terrestrial poles. It is necessarily less than the tem- 

 perature which belongs to the coldest countries; but in this comparison 

 we must consider only well ascertained observations, and not take in- 

 to account the accidental effects of a very intense cold, which might 

 be caused by evaporation, violent winds, and an unusual expansio 

 of the air.* 



" After having ascertained the existence of the fundamental tem- 

 perature of space, without which the effects of the heat observed on 

 the superficies of the globe would be inexplicable, we shall add, that 

 the origin of this phenomenon, if we may so speak, is evident. It is 

 owing to the irradiation of all the bodies of the universe, whose light 

 and heat can reach us. The stars which we perceive with the naked 

 eye, the innumerable multitude of stars seen with the telescope, and 

 of obscure bodies which fill the universe, the atmospheres which sur- 

 round these luminous bodies, the rarified matters spread in different 

 parts of space, concur in forming those rays which on all sides pe- 

 netrate the planetary regions. We cannot conceive the existence of 

 such a system of luminous, or heated bodies without admitting that 

 every point of the space which contains them, acquires a settled tem- 

 perature. 



" The immense number of the celestial bodies compensates for the 

 inequalities of their temperature, and renders the irradiation sensibly 

 uniform. 



" This temperature of space is not the same in the different regions 

 of the universe, but it does not vary in those in which the planetary 

 bodies are contained, because the dimensions of this space are without 

 comparison smaller than the distances which separate them from the 

 shining bodies. Thus in all points of the earth's orbit, this planet is 

 subject to the same temperature of the heavens. 



" It is the same with the other planets of our system : they all par- 

 take of the common temperature, which is more or less augmented for 

 each of them by the impression of the rays of the sun, according to 

 the distance of the planet from that orb." 



* This is the way in which we must explain the account given by Captain Parry, 

 who speaks of having observed a degree of cold of 50° at Melville Island. 



