THE PLANETS. 461 



slightly modify the climates of the individual zones, and that 

 in very long periods. Although the analyses which deter- 

 mine these limits accurately is not yet quite completed, still 

 so much, at least, follows from it, that the excentricity of the 

 Earth's orbit will never equal those of the orbits of Juno, 

 Pallas, and Victoria. 



10. Intensity of the Light of the Sun upon the Planets. If 

 the intensity of light upon the Earth is taken as = 1 , it will 

 be found to be upon the other planets, as follows : 



Mercury 6 "6 74 



Venus 1-911 



Mars 0-431 



Pallas 0-130 



Jupiter . . 036 



Saturn O'Oll 



Uranus 0-003 



Neptune O'OOl 



In consequence of the very great excentricity of their 

 orbits, the intensity of light on the following planets 

 varies in 



Mercury, in perihelion, 10*58 ; in aphelion, 4*59 

 Mars 0-52; 0*36 



Juno 0-25; 0-09 



while the Earth, owing to the slight excentricity of its orbits, 

 has in perihelion 1*034, and in aphelion 0'967. If the Sun- 

 light upon Mercury is seven times more intense than upon 



de Pallas." " As the excentricity always has been, and always 

 will be, very small, the influence of the secular variations of 

 the quantity of solar heat received by the Earth upon the 

 mean temperature would appear also to be very limited. It 

 cannot be admitted that the excentricity of the Earth, which 

 is actually about ^, has ever been, or ever will be ^ as that 

 of Juno or Pallas." 



