CONDITION OF THE LARGER PLANETS. 1 87 



"We are forced then to believe that there is some cause 

 at work to overcome the natural tendency of the 

 planet's mass. Doubtless this cause is the same which 

 operates to prevent the sun's mighty mass from 

 concentrating, as it would, into an intensely dense 

 -globe, were its gravitating energies left unresisted 

 viz., intense heat. The sun is, of course, very much 

 hotter than Jupiter and Saturn ; his . heat, indeed, 

 overcomes a very much greater contractive energy. 

 But Jupiter and Saturn must be very much hotter 

 than the earth. 



The third argument is based on the telescopic 

 evidence of the existence of a very deep cloud-laden 

 atmosphere surrounding each of the planets Jupiter 

 and Saturn. 



It is first to be noticed, as respects this argument, 

 that the general aspect of the belts of Jupiter (Saturn 

 is too far off for similar appearances to be noted) 

 indicates the presence of rounded masses of cloud 

 floating in a deep atmosphere. These rounded masses 

 can only be seen as such on the middle parts of the 

 disc, but there their appearance shows unmistakably 

 that they are really round that is, not merely round 

 in appearance, as a circle is round, but round as a 

 globe is round. No one who has studied Jupiter with 

 a powerful telescope can for a moment doubt that 

 some at least among the cloud-masses which are seen 

 in his disc are roughly globular in shape. It is suffi- 

 cient if only one of these masses has really had such a 

 shape, for though any number of flat objects may float 



