THE PLANETS, ARE THEY" INHABITED ? 



Fig. 4. 



sun's disk is diminished, or that the same effect would be pro- 

 duced by a proportionally increased sensibility of the retina. 

 In like manner the diminished calorific power of the sun's 

 rays proceeding from their dimi 

 nished density, might be compen- 

 sated by modified atmospheric con- 

 ditious, just as we find with the 

 same density of the solar rays all 

 climates in ascending on tropical 

 mountains to various altitudes from 

 the level of the sea to the line of 

 perpetual snow. 



These points have been already 

 so fully developed and explained, 

 that we need not here further insist 

 upon them. 



It is apparent, therefore, that 

 so far as the vastness of their 

 distances from the sun compared 

 with that of the earth affects the 

 illumination and warmth supplied 

 to them, there are no grounds for 

 concluding that they may not be 

 the habitations of races organised 

 in a manner not differing in any 

 important respect from those which 

 inhabit the earth. 



20. One of the most striking cir- 

 cumstances in which the group of 

 planets now under consideration 

 differ from the earth and the other 

 three which form the terrestrial or 

 inner group is their great compara- 

 jjjf live magnitude. The actual dia- 



meter of the earth is, in round 

 numbers, 8000 miles. That of 



Jupiter is 88,000, that of Saturn 



75,000, that of Uranus 35,000, and 

 N that of Neptune 37,500 miles. The 



diameter of Jupiter is therefore 

 11, that of Saturn 9|, that of Ura- 

 nus 4^, and that of Neptune 4| 

 times the diameter of the earth. 



But the volumes or bulks of globes being in the proportion ot 

 the cubes of their diameters, it follows that the bulk of Jupiter 

 26 



