CONDITION OF THE LARGER PLANETS. 
49 
For my own part, I think that the photometric evidence 
renders it very probable that a slight portion of the light of the 
planets Jupiter and Saturn is inherent; and I think the colour 
of the equatorial belt of Jupiter and its changes of colour cor- 
respond with this view. I should be disposed to assign, as the 
reflective power of Jupiter (his albedo , as Zollner calls it) about 
500, or more than twice the reflective power of white sandstone, 
and thus to attribute about one-fifth of Jupiter’s light to the 
planet’s inherent lustre. (In Saturn’s case Zollner’s observa- 
tions are much less satisfactory — his measures indeed of the 
planet’s total light were probably even more satisfactory than 
in Jupiter’s case, but it is exceedingly difficult to take properly 
into account the effect of the ring-system, which, though very 
much foreshortened when Zollner made his observations, must 
nevertheless have appreciably affected his results.) All the 
known facts accord well with this view. 
Certainly the spectroscopic evidence recently 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 spec- 
trum of Jupiter, which are known to belong to the absorption 
spectrum of aqueous vapour, the planet’s surface cannot be 
intensely hot. But Jupiter’s absorption spectrum belongs to 
layers of his atmosphere lying far above his surface. We can 
no more infer- — nay, we can far less infer — the actual tempera- 
ture of Jupiter’s surface from the temperature of the layers 
which produce his absorption spectrum, than a being who ap- 
proached our earth from without observing the low tempera- 
ture 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 are , 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 apparently irresistible argu- 
ments, and against which no known facts appear to afford any 
argument of force, should replace the ordinary theory, originated 
in a haphazard way, and in whose favour no single argument 
of weight has ever been adduced. Since it appears, — (1) that 
if the accepted theory of the development of our system is 
NEW SERIES, VOL. I. — NO. I. E 
