Elements of Astronomy. 17 



parent motion, according to the order of the signs, of 36",7 

 in a year, or 1° 34' 33",8 in a century. 



His orbit is incUned to the plane of the ecliptic in an 

 angle of 1° 18' 5l",5 : which is observed to decrease nearly 

 i22",fi in a century. 



His orbit, at the commencement of the present century, 

 crossed the ecliptic in 3' 8^ 25' 34",2. But the place of 

 the nodes lias an apparent motion in longitude, according 

 to the order of the signs, of 34",3 in a year, or 57' 1 2",4 in 

 a century. 



The rolatio7T on his axis is performed in Q*" 55' 49",7: 

 and his axis forms an angle of 86-' 54' 30",0 with the plane 

 of the ecliptic. 



[His mean diameter is equal to 91522 miles : consequently 

 he is about 11 i times as large as our Earth.] The axis of 

 his poles is to his equatorial diameter as -9287 to 1, or as 

 i3 to 14. 



His mass, compared with that of the Sun considered as 

 unity, is -^-^.-^i but his dejisity is '909501. 



[the proportion of light and heat, received from the Sun, 

 is -037: that received by the Earth being considered as 

 unity.] 



He IS surrounded by faint substances called zones or lelts; 

 which are supposed to be parts of his atmosphere. And he 

 is accompanied by four satellites. 



A body, which weighs one pound at the equatorial sur- 

 face of the Earth, would, if removed to the surface of Jupi- 

 ter, weigh 2-281 pounds. 



As seen from the Earth, the motion of Jupiter appears 

 sometimes to be retrograde. The mean arc which he de- 

 scribes in this case is about y'-' 54': and its mean duration 

 is about 121 days. This retrogradation commences, or 

 finishes, when the planet is not more distant than 115** 12' 

 from the Sun. 



His mean apparent equatorial diameter is 38"2: it is 

 greatest wL.n in opposition, at which time it is equal to 

 4 7", 6. 



Saturn. 



Saturn performs his sidereal revolution in 10758'' 23'' 

 r6'34",2; or in 29-456 Julian years. But this period is 

 subject to some inequalities. His mean synodical revolu- 

 tion is performed in about 378 days. 



ii\s mean distance from the Sun is 9*539; that of the 

 Earth being considered as unity. This majces his mean 

 distance above 890 millions of miles. 



Vol. 39. No. 165. Jan, 1812. B The 



