76 TEMPEKATUEE OF SPACE. [SECT. xxvi. 



the radiation of the earth. Lambert had proved that the 

 capacity of the atmosphere for heat varies according to the 

 same law with its capacity for absorbing a ray of light 

 passing through it from the zenith, whence M. Svanberg 

 found that the temperature of space is 58 below the zero 

 point of Fahrenheit's thermometer. From other researches, 

 founded upon the rate and quantity of atmospheric refrac- 

 tion, he obtained a result which only differs from the pre- 

 ceding by half a degree. M. Fourier has arrived at nearly 

 the same conclusion from the law of the radiation of the 

 heat of the terrestrial spheroid, on the hypothesis of its 

 having nearly attained its limit of temperature in cooling 

 'down from its supposed primitive state of fusion. The differ- 

 ence in the result of these three methods, totally independent 

 of one another, only amounts to the fraction of a degree. 



The cold endured by Sir Ed ward Parry one day, in Melville 

 Island, was 55 below zero; and that suffered by Captain 

 Back, on the 17th of January, 1834, in 62 46^' of north 

 latitude, was no less than 70 below the same point. How- 

 ever, M. Poisson attributes this to accidental circumstances, 

 and, by a recent computation, he makes the temperature of 

 space to be 8 above the zero of Fahrenheit. This he con- 

 siders greatly to exceed the temperature of the exterior 

 strata of the atmosphere, which he conceives to be deprived 

 of their elasticity by intense cold ; and he thus accounts for 

 the decrease of temperature at great elevations, and for the 

 limited extent of the atmosphere. 



Doubtless, the radiation of all the bodies in the universe 

 maintains the ethereal medium at a higher temperature 

 than it would otherwise have, and must eventually increase 

 it, but by a quantity so evanescent that it is hardly possible 

 to conceive a time when a change will become perceptible. 



The temperature of space being so low, it becomes a matter 

 of no small interest to ascertain whether the earth may not 

 be ultimately reduced by radiation to the temperature of the 

 surrounding medium; what the sources of heat are; and 



