PORTION OF THE COSMOS. THE PLANETS. 313 



distances from the Stm. The following table gives all 

 the planets discovered hitherto, with their mean distances 

 from the central body, taking, as has always been customary 

 in astronomy, the mean solar distance of the Earth (20682000 

 German, or 82728000 Eng. geographical miles) as unity. 

 In describing the planets separately, their greatest and least 

 distances from the sun will be given i. e. their distances 

 when in aphelion and in perihelion, or when the planet, in 

 the course of its motion in the ellipse of which the sun 

 occupies the focus, is respectively at either end of the major 

 axis (the line of the apsides), viz. the end which is farthest from, 

 or that which is nearest to, the focus. By the mean solar dis- 

 tance of a planet, which is that which we are now speaking 

 of, we understand the mean between the greatest and the least 

 distance, or half the major axis of the planet's orbit. The 

 numerical data already given, and also those which follow, 

 are taken for the most part from Hansen's careful recapitu- 

 lation of the planetary elements, in Schumacher's Jahrbuch 

 for 1837. Where the data are related to time, they apply, 

 in the case of the older- known and larger planets, to the year 

 1800, but in that of Neptune to 1851 : the Berlin Astrono- 

 mische Jahrbuch for 1853 has also been made use of. For 

 the statements relating to the smaller planets I am indebted 

 to the friendship of Dr. Galle ; they all refer to very recent 

 epochs. 



Distances of the planets from the Sun : 



Mercury 0'38709 



Yenus 0*72333 



Earth 1-00000 



Mars 1-52369 



