THEORETICAL ASTRONOMY. 119 
Lhe following table exhibits the Relative Volumes of the Sun and Planets. 
ee eee eeeeEE——EEEE—EEE——E———————EE SE 
Planet Actual Volume in Mion of |. Rasi of rma Volumes of the 
Sun, 14,966,309,588 1 1 
Jupiter, 15,039,700 1 995 
Saturn, 7,817,666 bt 1914 
Uranus, 872,175 1 17,160 
Earth, 10,636; 1 1,407,122 
Venus, | 10,2108, | 1: 1,465,733 
Mars, 1489 by: 10,052,599 
Mercury, 638 ae 23,458,165 
Pallas, 180, | 1 82,778,261 
Ceres, 85 1 176,489,500 
Juno, | 5375 | ae 281,321,609 
Vesta, | #, | 1 : 288,101,459,569 
37. Pl. 14, figs. 12-15, gives the four principal positions of Saturn and 
his rings, with respect to our earth, as they are perceived during the 293 
years’ revolution of Saturn about the sun. Fig. 12 gives a view of Saturn 
and his rings at the time this planet is situated in the sign of Cancer () ; 
jig. 13 represents them when—14# years later—Saturn is found in the 
sign of Capricornus w; fig. 14, when in the sign of Libra +; and fig. 15, 
when—14# years later—he is found in Aries °. 
The dimensions of the rings, as also their distances from each other and 
from Saturn, will be found in sec. 58. This ring system is, however, no 
great source of gratification to the inhabitants of Saturn, as it is only visible 
in the middle equatorial regions of the planet. It does not shine by night, 
only during the day, or a little while after sunset and before sunrise, and 
even this in general only during the summer. For at night the whole ring is 
shaded by Saturn; and in winter, instead of illuminating the planet, it casts 
a shadow upon the side of the planet opposite to the sun, covering an area 
of many millions of miles, and lasting in part almost fifteen of our years. 
On the other hand, the inhabitants of the surface of the ring will perceive 
Saturn’s hemisphere in their horizon, of enormous size, and should they be 
on the very edge of the ring, they will perceive the planet in their zenith 
about 20,000 times larger than the sun. The floor itself upon which they 
stand, reaches to the right and to the left, visible up to the heavens, closing 
beyond the planet, thus affording beyond all question an entirely unique 
and most magnificent spectacle. 
38. Every planet revolving about the sun must have at one time a 
period of least, and at another one of greatest distance from the earth. In 
the first case the planet is said to be in its perigee, in the second in its 
apogee. The two inferior planets, Mercury and Venus, are in their perigee 
at inferior conjunction, and in their apogee at superior conjunction; the 
superior planets are in apogee at conjunction, and in perigee at opposition 
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