THE PLANETS, ARE THEY INHABITED ? 



By comparing their real diameters with their distances, the 

 apparent diameters of the several satellites, as seen from Jupiter, 

 may be easily ascertained. 



18. The first satellite has an apparent diameter equal to that of 

 the moon ; the second and third are nearly equal and about half 

 that diameter ; and the apparent diameter of the other satellite 

 is about the fourth part of that of the moon. 



It may be easily imagined what various and interesting 

 nocturnal phenomena are witnessed by the inhabitants of Jupiter, 

 when the various magnitudes of these four moons are combined 

 with the quick succession of their phases and the rapid apparent 

 motions of the first and second. 



The motions of the first three satellites are so related that 

 they never can be at the same time on the same side of Jupiter ; 

 so that whenever any one of them is absent from the Jovian 

 firmament at night, one at least of the others must be present. 

 The nights are, therefore, always moonlit, except during 

 eclipses, and often enlightened at once by three moons of different 

 apparent magnitudes, and seen under different phases. 



19. Of all the planets either of this or the terrestrial group, 

 that which presents to the astronomical observer the most 

 astonishing spectacle is Saturn a stupendous globe, nearly 900 

 times greater in volume than the earth, surrounded by two, at 

 least, and probably by several thin flat rings of solid matter, 

 outside which revolve a group of eight moons ; this entire system 

 moving with a common motion so exactly maintained that no 

 one part falls upon, overtakes, or is overtaken by another in 

 their course around the sun. 



Such is the SATURNIAN SYSTEM, the central body of which was 

 known as a planet to the ancients, the annular appendages and 

 satellites being the discovery of modern times. 



The distance of Saturn from the sun is so enormous that if 

 the whole earth's orbit, measuring nearly 200,000000 of miles in 

 diameter, were filled with a sun, that sun seen from Saturn 

 would be only about 24 times greater in its apparent diameter 

 than is the actual sun seen from tha/earj^ A cannon-ball 

 moving at 500 miles an hour would take -0.1 00(3 j?eajs^ and a 

 ^ railway train moving 50 miles an hour would take 10000 years 

 to move from Saturn to the sun. Light, which moves at the 

 rate of nearly 200000 miles per second, takes 4. days 1^ hours' and 

 /S 3 minutes to move over the same distance. Yet to this distance 

 solar gravitation transmits its mandates, and is obeyed with the 

 utmost promptitude and the most unerring precision. 



Taking the diameter of Saturn's orbit at 1800,000000 of 

 miles, its circumference is 5650,000000 of miles, over which it 

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