CONDITION OF THE LARGER PLANETS. 197 



Certainly the spectroscopic evidence obtained by 

 Vogel, or rather the general spectroscopic evidence (for 

 his results are not new) is not opposed, as he seems 

 to imagine, to the theory that the actual surface of 

 Jupiter is intensely hot. His argument is that, because 

 dark lines are seen in the spectrum of Jupiter, which 

 are known to belong to the absorption spectrum of 

 aqueous vapour, the planet's surface cannot be in- 

 tensely hot. But Jupiter's absorption spectrum be- 

 longs to layers of his atmosphere lying far above his 

 surface. We can no more infer nay, we can far less 

 infer the actual temperature of Jupiter's surface from 

 the temperature of the layers which produce his 

 absorption spectrum, than a being who approached our 

 earth from without observing the low temperature of 

 the air ten or twelve miles above the sea-level could 

 infer thence the temperature of the earth's surface. 

 There may be, in my opinion there almost certainly 

 we, layers of cloud several thousand miles deep between 

 the surface we see and the real surface of the planet. 

 I do not suppose that the inherent light referred to 

 above as probably received from Jupiter, is light coming 

 directly from his glowing surface, but the glow of cloud 

 masses high above his surface, and illuminated by it 

 perhaps even the glow of cloud-layers lit up by lower 

 cloud-layers which themselves even may not receive 

 the direct light emitted by his real surface. 



To sum up, it appears to me, that a theory to 

 which we are led by many effective and some appa- 

 rently irresistible arguments, and against which no 



