THE PLANETS. 107 



while the volume of'the Sun is to that of the Earths 1 107 124. 

 Small alterations in the measurements of the diameters in- 

 crease 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 disks and their proximity, by the color of their light, 

 by scintillation — which is not entirely wanting to some plan- 

 ets, in certain positions — and by the peculiarity with which 

 their different surfaces reflect the Sun's light. Whether 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 plan- 

 etary system as a whole, so far as it is yet known, and to rep- 

 resent 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 (20,682,000 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 added 

 afterward, when treating of the planets individually. By the 

 mean distance from the Sun, of which alone mention will be 

 made in this place, is to be understood, the mean of the great- 

 est and smallest distance, or the half major axis of the plan- 

 et's orbit. It must also be observed, that the numerical data 

 employed, both previously and hereafter, are for the most part 

 taken from Hausen's careful classification of the planetary 

 elements in Schumacher's Jahrbuch for 1837. Where the 

 data refer to time, they are, in the case of the older and larger 

 planets, for the year 1800 ; but in the case of Neptune, for 

 the year 1851, by the aid of the Berlin astronomisclien Jahr- 

 buch of 1853. The comparison of the small planets occur- 

 ring afterward, and for which I am indebted to Dr. Galle, 

 refers exclusively to more recent epochs. 



Distances of the Planets from the Sun. 



Mercury 0*38709 I Earth 1-00000 



Venus 0-72333 Mars 1 52369 



