CONDITION OF THE LARGER PLANETS. 
43 
reach the earth’s present condition of development would exceed 
the time during which our earth has endured, from her begin- 
ning until now, six times, even though Jupiter at his beginning 
were no hotter than the earth. As he was certainly much 
hotter, it may fairly be said that he would require thousands of 
millions of years to reach the stage which the earth has reached 
after hundreds of millions of years ; and that, if the two planets 
were both fashioned at the same time, Jupiter must still 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 first 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 1250 times, but a mass only exceeding hers 340 
times. Saturn’s volume exceeds the earth’s 7 00 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. We 
are forced then to believe that there is some cause at work to 
overcome the natural tendency of the planet’s mass. Doubtless 
this cause is the same which operates to prevent the sun’s mighty 
mass from concentrating, as it would, into an intensely dense 
globe, were its gravitating energies left unresisted — viz., intense 
heat. The sun is, of course, very much hotter than Jupiter 
and Saturn ; his heat, indeed, overcomes a very much greater 
contractive energy. But Jupiter and Saturn must be very much 
hotter than the earth. 
The third argument is based on the telescopic evidence of 
the existence of a very deep cloud-laden atmosphere surround- 
ing each of the planets Jupiter and Saturn. 
It is first to be noticed, as respects this argument, that the 
