46 THE POPULAR SCIENCE MONTHLY. 



see that the sun is in a state of intense heat, and we know that this 

 heat produces effects antagonistic, as it were, to those produced by the 

 attraction of his mass as a whole upon every portion of his substance. 

 But, if we make no similar assumption in Saturn's case, we find his 

 small density inexplicable. 



Another circumstance associated with the question of Saturn's den- 

 sity introduces new difficulties of the most perplexing nature if it be 

 regarded according to the ordinary view, while it seems not only ex- 

 plicable, but manifestly to be expected, on the theory that Saturn's 

 whole orb is in an intensely heated condition. Saturn certainly has 

 an atmosphere of considerable depth. The belts which surround his 

 globe are evidently produced by clouds in his atmosphere, though 

 what the nature of these clouds may be is not as yet known. The 

 brighter belts are the cloud-belts, while the darker either show his 

 real surface, or, far more probably, belong simply to lower cloud- 

 layers. These belts are variable in appearance and position, some- 

 times changing with great rapidity. Their real extent is enormous, 

 exceeding the whole surface of our earth, even in the case of the nar- 

 rowest belts yet seen. No one who has viewed them through tele- 

 scopes of great power can refuse to adopt the conclusion that the at- 

 mosphere in which these great cloud-zones are suspended must be of 

 great depth, certainly far deeper than our atmosphere. But such an 

 atmosphere, subjected to the attractions of Saturn's mass, would be 

 enormously compressed underneath those manifestly thick cloud-lay- 

 ers. A very moderate assumption as to the depth of the atmosphere 

 would lead to the conclusion that at its base it must be denser than 

 water — that is, denser than Saturn himself. No gas could exist as 

 gas at this density. Apart from this, we are here arriving at the 

 very theory which the ordinary view of Saturn teaches us to avoid — 

 viz., the theory that he is utterly unlike our earth in physical condi- 

 tion. We may much more conveniently arrive at the same general 

 conclusion, while avoiding other difficulties, by simply adopting the 

 same explanation in this case which serves to account also for the 

 small density of Saturn's mass — viz., the theory that Saturn's globe is 

 in a state of intense heat. 



But now let it be noticed how perfectly this view of Saturn's con 

 dition accords with the theories which are beginning to be established 

 respecting the genesis of the solar system. Whether we regard the 

 planets as formed from the condensation of enormous nebulous masses, 

 or whether we assume that they were produced by the gathering to- 

 gether of matter originally traveling in dense meteoric flights around 

 the central aggregation whence the sun was one day to be formed, we 

 see that the larger the planet the greater must have been its origiual 

 heat. The heat generated during the condensation of a nebulous mass 

 must depend upon the magnitude of the mass, since in fact the ac- 

 cepted theory of heat teaches us that the original heat of a globe so 



