234 T^^ POPULAR SCIENCE MONTHLY. 



ance of those planets, the condition of the atmosphere above the 

 clouds may be left out of the consideration. Let us assume the den- 

 sity of the atmosphere at the upper surface of the clouds to be equal 

 to that of our atmosphere at the height of about fifteen miles, and we 

 shall perhaps regard it as sufficiently rare. The height of the upper 

 cloud-layers above the surface proper of the planets will now depend 

 on the surface-temperature and on the mass of the atmosphere. The 

 Ixw of density for different heights above the surface of the planets is 

 almost independent of the mass of the atmosphere, unless we consider 

 the mass as very great in comparison with that of the planet which it 

 surrounds. 



Let us suppose the density of the atmosphere at the surface of the 

 planet to be equal to that of water and such a density is certainly 

 too great for either Jupiter or Saturn it is then possible for us to cal- 

 culate the height of the cloud-layers to which we have already re- 

 ferred, if the temperature be given ; or, if the height be given, to cal- 

 culate the temperature of the surface of the planet. We have seen it 

 suggested that, if this height be assumed equal to 2,000 miles, it will 

 enable us to explain the telescopic appearances of Jupiter and Saturn. 

 This height for the former planet requires a surface-temperature of 

 45,000*^, and for the latter 20,000 Fahr. It seems to be quite evident 

 that these temperatures are much too high. That Jupiter and Saturn 

 give out more light than they receive from the sun, seems nearly cer- 

 tain; but a temperature of 20,000 would seem to imply a much greater 

 intrinsic splendor than either Jupiter or Saturn possesses.* 



Prof. Proctor, in one of his articles, assumes the height of the 

 highest cloud-layers to be 100 miles above the surface of the planet. 

 This implies a temperature of 1,800 for the surface of Jupiter, and 

 of 600 for that of Saturn. We must now conclude that the cloud- 

 layers which form the outlines of the disks of Jupiter and Saturn are 

 scarcely 100 miles high on Saturn, and considerably less on Jupiter; 

 for we have assumed the surface-density much too high, and probably 

 the density of the upper cloud-layers much too small. We cannot 

 certainly consider the temperature of either planet above 2,000 

 Fahr. 



The Herschelian figure of Saturn can probably be explained by the 

 surface cloud-layers in its atmosphere. We need a greater number 

 of and more careful observations on Jupiter and Saturn. 



* These calculations are based on a mathematical paper read before the American 

 Philosophical Society, November 3, 1876. 



