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POPULAR SCIENCE REVIEW. 
true, the large planets must of necessity be far younger, that is 
hotter, than our earth and other small planets; (2) that if 
made of similar materials, those planets must of necessity be 
far denser than they actually are, unless they are very much 
hotter than the earth ; (3) that the atmospheres (judging of 
their depth from the planet’s appearance) would be compressed 
into solid and very dense matter under the planet’s attraction 
unless exceedingly hot throughout their lower layers ; (4) that 
the belts and their changes imply the uprush and down rush of 
heated masses of vapour through enormous depths of atmo- 
sphere ; (5) that the cloud-belts neither change with the progress 
of the day nor of the year in the large planets, but in a manner 
in no way referrible to the sun, and are therefore presumably 
raised by the intense heat of the planet’s own substance ; (6) 
that so remarkable are the changes taking place in the atmo- 
spheres of Jupiter and Saturn, as appreciably (even at our 
enormous distance) to affect the figure of those planets ; and 
(7) that the planets shine with more than 2J times the bright- 
ness they would have if their visible surface were formed of 
even so lustrous a substance as white sandstone — I think the 
conclusion is to all intents and purposes demonstrated that the 
planets Jupiter and Saturn really are in a state of intense heat. 
If they ever are to be the abode of life, they will probably not be 
ready to subserve that purpose for hundreds of millions of years. 
i 
