102 THE BORDERLAND OF SCIENCE. 



is not displaced at all during the long Saturnian year. 

 It remains always persistently equatorial! Nothing 

 could be more easy than the detection of its change of 

 place if it followed the sun ; yet no observer has ever 

 suspected the slightest degree of systematic change cor- 

 responding with the changes of the Saturnian seasons. 

 Or rather, it is absolutely certain that no such change 

 takes place. 



It appears, then, that night and day, and summer 

 and winter, are alike without influence on the Jovian 

 and Saturnian cloud zones. Can it reasonably be ques- 

 tioned that, this being the case, we must look for the 

 origin of the cloud zones in these planets themselves, 

 and not in the solar orb, whose action must needs be 

 largely influenced by the alternation of night and day 

 and of the seasons ? 



But further, we find that a circumstance which had 

 seemed perplexing when we compared the Jovian belts 

 with terrestrial trade-wind zones, finds an explanation 

 at once when we regard the belts as due to some form 

 of action exerted by the planet itself. For let us sup- 

 pose that streams of vapour are poured upwards to vast 

 heights and with great velocity from the true surface 

 of the planet. Then such streams starting from the 

 surface with the rotational movement there prevailing, 

 would be carried to regions where (owing to increase of 

 distance from the centre) the movement due to the 

 planet's rotation would be greater. They would thus 

 be caught by the more swiftly-moving upper air and 

 carried forwards, the modus operandi being the reverse 



