218 M. Arago on the Therrtiometrical State 



with perpetual snows, and also the rapid diminution of the tem- 

 perature of the atmosphere, as observed by aeronauts in their 

 ascents, meteorologists had imagined, that in those regions 

 whence the extreme rarity of the air will ever exclude man, in 

 those beyond the atmosphere especially, there must ever reign 

 immeasurable cold. It was not only by hundreds but by thou- 

 sands of degrees, that they had undertaken to measure it. But 

 all this was most foolish exaggeration. The hundreds and the 

 thousands of degrees have descended, under the strict examina- 

 tion of Fourier, to some 50° or 60° cent. 60° or 60° cent, be- 

 low zero is the temperature of those spaces in which the earth 

 revolves from year to year; and such is the degree that the ther- 

 mometer would indicate in the whole region occupied by our 

 system, if the sun and the planets which accompany it were to 

 cease to be. 



Fourier has arrived at this conclusion, whilst he was inquir- 

 ing what phenomena would be observed if the earth were placed 

 in a space deprived of all heat. According to this hypothesis, 

 he remarks, that the Polar Regions would be subjected to an ex- 

 tent of cold much greater than actual observation indicates. 

 The alternating of day and night would produce most sudden 

 effects, and of vast intensity, &c. &c. 



It is most desirable, that the memoir in which the learned Se- 

 cretary of the Academy must have recorded the proofs of these 

 important propositions, should not be lost, and that it should be 

 speedily presented to the public. 



The heat of celestial spaces*, whatsoever may be its intensity, 

 is probably owing to the radiation from all the bodies in the 

 universe whose light reaches us. Many of these bodies have 

 disappeared ; others only present not unequivocal marks of fad- 

 ing ; others, again, increase in splendour ; but these are the rare 

 exceptions. But as the total number of stars and nebulae, that 

 are visible with the aid of telescopes, certainly surpasses many 

 thousands of millions, we have every reason to believe that, from 

 this side at least, the inhabitants of the terrestrial globe have no 

 serious alteration of climate to apprehend. 



• Lei no one be surprised at the use of the term heat^ in speaking of 50° or 

 60° cent, below zero. This is no more than the temperature that Captain Parry 

 and Franklin have weathered in their voyages to the Polar Regions ; and 



