1 86 LIGHT SCIENCE FOR LEISURE HOURS. 



require thousands of millions of years before he will 

 have attained to that stage of planetary life through 

 which our earth is now passing. Saturn would not be 

 so far in the rear of our earth because his mass does 

 not exceed hers so greatly. Still he contains nearly a 

 hundred times as much matter, and must be regarded 

 as in all probability, so far as this argument alone is 

 concerned, hundreds of millions of years behind our 

 earth in point of development. 



The second argument is that derived from the 

 small density of Jupiter and Saturn. Jupiter has a 

 volume exceeding the earth's about 1,250 times, but a 

 mass only exceeding hers 340 times. Saturn's volume 

 exceeds the earth's 700 times, his mass only 99 times. 

 Jupiter's mean density is therefore about one-fourth, 

 Saturn's about one-seventh, of the earth's. Science 

 no longer accepts the belief that either planet is 

 formed in the main of different materials, spectroscopic 

 analysis having demonstrated the existence of a general 

 uniformity of structure throughout the solar system. 

 Neither can science any longer admit the possibility 

 that Jupiter and Saturn are hollow globes, experiment 

 having proved that under the pressure exerted by the 

 mass of either planet, a substance a hundred times 

 stronger than the strongest steel would be perfectly 

 plastic throughout the greater portion of either planet's 

 interior, so that hollow spaces, if they could be formed 

 for a moment, would fill up just as an open space 

 formed for a moment by thrusting water on one side 

 fills up as the water flows back to its normal position. 



