SATURNIAN SYSTEM. 



moves in 10759 days. Its daily motion is therefore 525140 

 miles, and its hourly 21880 miles. 



20. All that has been said above respecting the atmosphere, the 

 diurnal rotation, and their consequences, the clouds, atmospheric 

 currents, trade-winds, and oblate figure in the case of Jupiter, 

 may be applied without any important modification to Saturn. 



This planet is attended by eight moons, four of which, like 

 those of Jupiter, are remarkable for their proximity to the 

 planet, three being at distances considerably less than that of 

 the terrestrial moon from the earth, and the fourth at nearly 

 the same distance. Of the four other moons, the most remote 

 is ten times further from Saturn than the terrestrial moon 

 is from the earth, and the nearest is about one half more 

 distant. 



The distances of moons are, however, more justly estimated 

 relatively to the planets they attend, by expressing them in 

 semi-diameters of the planet. If thus expressed, the moons of 

 Saturn are on a scale of distance very much less than that of 

 the terrestrial moon. The distance of the most remote is 

 64 semi-diameters of Saturn, while that of the nearest is little 

 more than 3 semi-diameters. The distance of the terrestrial 

 moon from the earth is 60 semi-diameters. 



Great, however, as these distances are, they are reduced to 

 a very small apparent measure, owing to the remoteness of the 

 Saturnian system from^the earth. If the centre of the terres- 

 trial moon were to come upon the centre of Saturn's disc, the 

 most remote of his satellites could not approach nearer to the 

 edge of the moon's disc than one-third of the moon's semi- 

 diameter. Thus, although the Saturnian system fills a space 

 measuring about 5,000000 of miles in its extreme breadth, this 

 entire space would be covered by the moon's disc, even if that 

 disc had a diameter one-third less than its actual diameter. 



All that has been said of the phases and appearances of the 

 moons of Jupiter, as presented to the inhabitants of that planet, 

 is equally applicable to the satellites of Saturn, with this dif- 

 ference, that instead of four, there are eight moons continually 

 revolving round the planet, and exhibiting all the monthly 

 changes to which we are accustomed in the case of the solitary 

 satellite of the earth. 



The periods of Saturn's moons, like those of Jupiter, are short, 

 with the exception of those most remote from the primary. The 

 nearest passes through all its phases in 22^ hours, and the fourth, 

 counting outwards, in less than 66 hours. The next three have 

 months varying from 4 to 22 terrestrial days. 



These seven moons move in orbits whose planes are nearly 



47 



