A GIANT PLANET. 103 



of that observed when an engine leaves a trail of con- 

 densed steam behind it; or rather, it may be compared to 

 what would take place if a steam-engine 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 atmosphere 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 

 dispersion, since the best telescopes, and notably Mr. 

 Buckingham's fine 21 -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 a first view too bizarre 

 to be entertained even for a moment. We have been 

 so accustomed to regard Jupiter and Saturn as other 

 worlds, that the mind is disposed to reject the concep- 

 tion that they can be so intensely heated as to be 

 utterly unfit to be the abode of living creatures. 



