THE PLANETS. 429 



The volumes of the planets in relation to the eartn arc 



diameters increase the data of volumes in the ratio of their 

 cubes. 



The moving planets which agreeably enliven the aspect of 

 the heavens, influence us simultaneously by the magnitudes 

 of their discs and their proximity, by the colour of their 

 light, by scintillation, which is not entirely wanting to some 

 planets, in certain positions and by the peculiarity with 

 which their different surfaces reflect the Sun's light. Whe- 

 ther a feeble evolution of light from the planets themselves 

 modifies the intensity and properties of their light, is a 

 problem which still remains to be solved. 



4. Arrangement of the Planets and their Distances from 

 the Sun. In order to form a general conception of the 

 planetary system as a whole, so far as it is yet known, and 

 to represent it in its mean distances from the central body, 

 the Sun, the following table is given, in which, as has always 

 been the custom in astronomy, the mean distance of the 

 Earth from the Sun (82728000 geographical miles) is taken as 

 unity. The greatest and smallest distances of the individual 

 planets from the Sun in aphelion and perihelion, according 

 as the planet is situated in the ellipse whose focus is occupied 

 by the Sun, at that point of the major axis (line of apsides) 

 which is the farthest from or nearest to the focus, will be 



