JUPITER'S MOONS. 



531 



Fig. 589 Jupiter. 



illustration of the planet. He is the biggest, and the brightest, except Venus 

 of all the planets. He revolves at a dis- 

 tance of 476,000,000 of miles from the sun, 

 and his year is equal to nearly twelve of 

 ours, while his day is scarcely ten hours long, 

 showing a rapidity more than twenty times 

 the rate of our earth. Jupiter, therefore, must 

 have a very much greater diameter than the 

 earth. 



There is much less sunlight and heat 

 found on Jupiter than upon Earth, because he 

 is so much farther from the sun than we are, 

 but at the same time the heat comes at less 

 intervals than with us. And here the theory 

 already noticed respecting the gradual cool- 

 ing of the planets will be remembered. Jupiter, 

 we can easily imagine, would take much 

 longer to get cool than Mars or the earth, 

 and, though his rapid rotation would assist 

 him, he must be still in the midst of a glow- 

 ing atmosphere without form and void perhaps a furnace for cloud and 

 vapour generation. 



Now when Jupiter is examined with the telescope it will be seen that 

 he is crossed by belts of vapour (see also page 489); and when we consider 

 the results of the spectrum analysis of the planet, we may fairly assume that 

 Jupiter is in a very heated state, and that we cannot really perceive the 

 actual body of the planet at all yet. There is an immense quantity of 

 water thus surrounding Jupiter, and he is still in the condition in which our 

 earth was before geology grasps its state, and long ere vegetation or life 

 appeared. The waters have yet to be " gathered together into one place," 

 and the dry land has yet to appear upon Jupiter, who is a very juvenile, if a 

 very enormous planet. Under these conditions we can safely assume that 

 there are no inhabitants of Jupiter. 



The belts, or zones, of Jupiter vary in hue, and the continual changes 

 which are taking place in this cloud region tend to show that disturbances 

 of great magnitude and importance are occurring. 



It is useless to speculate upon what will happen in Jupiter when the 

 disc is eventually cooled. The planet, we know, has not nearly reached 

 maturity ; the earth is in the full prime of its life, and the moon is dead and 

 deserted. What the millions of years which must elapse before Jupiter has 

 cooled may bring forth we need not try to find out. The earth will then, in 

 all probability, be as dreary as the moon is now, and we shall have returned 

 to dust. 



