238 ATMOSPHERE OF THE MOON. JECT. XXVL 



SECTION XXVI. 



Atmosphere of the Planets and the Moon Constitution of the Sun Esti- 

 mation of the Sun's tight His Influence on the different Planets 

 Temperature of Space Internal Heat of the Earth Zone of Constant 

 Temperature Heat increases with the Depth Heat in Mines and 

 Wells Thermal Springs Central Heat Volcanic Action The Heat 

 above the Zone of Constant Temperature entirely from the Sun The 

 Quantity of Heat annually received from the Sun Isogeothermal Lines 

 Distribution of Heat on the Earth Climate Line of Perpetual Con- 

 gelation Causes affecting Climate Isothermal Lines Excessive Cli- 

 mates The same Quantity of Heat annually received and radiated by 

 the Earth. 



THE ocean of light and heat perpetually flowing from 

 the sun, must affect the bodies of the system very differ- 

 ently, on account of the varieties in their atmospheres, 

 some of which appear to be very extensive and dense. 

 According to the observations of Schroeter, the atmos- 

 phere of Ceres is more than 668 miles high, and that of 

 Pallas has an elevation of 465 miles. These must re- 

 fract the light and prevent the radiation of heat like our 

 own. But it is remarkable that not a trace of atmosphere 

 can be perceived in Vesta. The action of the sun's rays 

 must be very different on such bodies from what it is 

 on the earth, and the heat imparted to them quickly 

 lost by radiation ; yet it is impossible to estimate their 

 temperature, since the cold may be counteracted by 

 their central heat, if, as there is reason to presume, they 

 have originally been in a state of fusion, possibly of 

 vapor. The attraction of the earth has probably de- 

 prived the moon of hers ; for the refractive power of 

 the air at the surface of the earth is at least a thousand 

 times as great as refraction at the surface of the moon. 

 The lunar atmosphere, therefore, must be of a greater 

 degree of rarity than can be produced by our best air- 

 pumps ; consequently no terrestrial animal could exist 

 in it. This was confirmed by M. Arago's observations 

 during the last great solar eclipse, when no trace of a 

 lunar atmosphere was to be seen. 



The sun has a very dense atmosphere, which is 

 probably the cause of the peculiar phenomena in his 

 photographic image already mentioned. What his body 

 may be, it is impossible to conjecture ; but he seems to 



