The Primary Planets. 289 



than that of the earth, and those inferior planets 

 whose distance is less than that of the earth. 



The superior planets are, Mars, Ceres, Pallas, 

 Juno, Vesta, Jupiter, Saturn, and Uranus, which 

 are further from the sun than the earth is, and 

 which, consequently, environ the latter in their 

 revolution : it is for this reason we see them some- 

 times on one side of the sun, and sometimes on 

 the other. The inferior planets are, Mercury 

 and Venus, which are nearer the sun than the 

 earth, x and which, consequently 5 never environ 

 the latter in their revolution. On this account 

 we see them always on the same side as the sun, 

 and never in opposition, because this earth is 

 never between them and the sun, 



It has been already stated that the apparent 

 diameter of the sun, viewed at his mean distance 

 from the earth, is 32' 3' '3. The apparent dia- 

 meters of the planets seen from the earth bear a 

 relation to their real size, and the distance of 

 <each. But, in comparing these diameters with 

 one another, or with that of the sun, they are 

 supposed to be seen all at a distance equal to the 

 mean distance of the earth from the sun, as in 

 the following table. 



VOL. I. 



