SKCT. xxvi.] ATMOSPHERE OF THE MOON. 273 



SECTION XXVI. 



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

 tion of the Sun's Light His influence on the different Planets Tempera- 

 ture 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 Con- 

 stant 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 Congelation Causes affecting Climate 

 Isothermal Lines Excessive Climates 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 differently, 

 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 atmosphere of Ceres 

 is more than 668 miles high, and that of Pallas has an 

 elevation of 465 miles. These must refract the light and 

 prevent the radiation of heat like our own. But it is re- 

 markable that not a trace of atmosphere can be perceived 

 in Vesta. The action of the sun's rays must be very dif- 

 ferent 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 vapour. The attraction of the earth 

 has probably deprived 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 



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