A GIANT PLANET. 29 q 







starting from the surface with the rational movement there prevailing, 

 would be carried to regions where (owing to increase of distance from 

 the centre) the movement due to the planet's rotation would be great- 

 er. They would thus be caught by the more swiftly-moving upper air 

 and carried forward, the modus operandi being the reverse of that ob- 

 served when an engine leaves a trail of condensed steam behind it ; 

 or, rather, it may be compared to what would take place if a steam-en- 

 gine were moving in the same direction as the wind, but less swiftly, 

 so that steam-clouds would be carried in front instead of behind. 



Now, heat is the only form of force which could account for the 

 formation of the enormous masses of cloud suspended in the atmos- 

 phere of Jupiter. And it seems difficult to conceive that the clouds 

 could be maintained at a great height above the real surface of the 

 planet, unless that surface were intensely hot as hot perhaps as red- 

 hot iron. If we supposed this to be the case, we should find at once an 

 explanation of the ruddy aspect of the dark belts. Nor would the 

 change of the great equatorial belt from white to red imply more than 

 that, owing to some unknown cause, clouds had not formed during the 

 last two years over the planet's equatorial zone, or, having formed, had 

 been dispersed in some way. We need not even imagine a complete dis- 

 persion, since the best telescopes, and notably Mr. Buckingham's fine 

 twenty-one-inch refractor, have shown always a multitude of minute 

 cloud-like objects over the ruddy equatorial zone. 



But the idea of a red-hot planet, or of a planet partially red-hot, 

 will appear at first view too bizarre to be entertained even for a mo- 

 ment. We have been so accustomed to regard Jupiter and Saturn as 

 other worlds, that the mind is disposed to reject the conception that 

 they can be so intensely heated as to be utterly unfit to be the abode 

 of living creatures. 



This unwillingness to accept startling ideas is not to be altogether 

 reprehended, since it prevents the mind from forming rash and baseless 

 speculations. Yet we must not suffer this mental habitude, excellent 

 though it may be in its proper place, to interfere with the admission 

 of conclusions which seem based on trustworthy evidence. Let us, then, 

 inquire whether the startling hypothesis to which we have been led 

 by the study or observed facts may not be found to be in agreement 

 with other facts not yet considered. 



It will be obvious that, if the real globe of Jupiter is thus intensely 

 heated, a portion of the planet's light must be inherent. Therefore we 

 might expect that the planet would shine somewhat more brightly than 

 a globe of equal size and similarly placed, shining merely by reflecting 

 the sun's light. Now, two series of good observations have been made 

 upon the luminosity of Jupiter. One was made by the late Prof. 

 Bond, of America, the other by Dr. Zollner, of Germany. According 

 to the former, Jupiter shines more brightly than he would if he re- 

 flected the whole of the light falling upon him ! According to the 



