114 SATURN. 



the earth ; for an eclipse of one of these satellites appears 

 to us to take place sixteen minutes sooner, when the 

 earth is in the part of her orbit nearest Jupiter, than when 

 in the part farthest from him. Hence light is sixteen minutes 

 in crossing the earth's orbit, and of course eight minutes in 

 coming from the sun. An observer on Jupiter, with eyes 

 constructed like ours, could never see Mercury, Venus, the 

 Earth, or Mars, for, on account of the immense distance, 

 they are always immersed in the sun's rays. 



QcTESTiONS. — 1. What is the diameter of Jupiter ? — distance from 

 the sun P — time of revolution round the sun ? — diurnal rotation ? 2 

 Describe the telescopic appearance of Jupiter. 3. What is the posi* 

 tion of his axis, and the consequence of that position ? 4. What a 

 said of Jupiter's moons ? 5. Of what use are their eclipses ? C. To 

 w^hat discovery have they led ? — how ? 



LESSON 52. 



Saturn and Uranus. 



Anoni'aly, irregularity, deviation from rule. 



Hypoth'esis, a supposition, a system formed under some principle 

 not proved. 



Saturn though not so brilliant as Jupiter, is a very con- 

 spicuous planet. It shines with a pale light, and the degree 

 of heat and light is eighty times less than at the earth. It 

 revolves round the sun in little less than thirty years, at the 

 mean distance of nine hundred millions of miles. It turns 

 on its axis in little more than ten hours, and its diameter is 

 seventy-nine thousand miles. 



Saturn, as seen through a good telescope, is a beautifu. 

 object, having seven moons, a double ring, and appearances 

 similar to the belts of Jupiter. The ring is one of the 

 greatest anomalies in our system. It is a thin, broad, opaque, 

 circular body, encompassing the planet without touching it, 

 like the wooden horizon of an artificial globe. Although 

 the phenomenon is usually termed the ring, yet it consists. 

 of two, entirely detached from each otV.er and from the body 

 of the planet, one exactly without or beyond the other. 

 Stars have been seen through the vacancy between them, 

 and also .between the inner ring and the planet. Concern; 



ni 



