14 The Saturnian System. (January, 
(noting always, however, that they must be quite unlike the 
seasons of our earth) are of a marked character, whereas 
Jupiter has scarcely any seasonal changes at all. Here, 
then, is a criterion to show what part, if any, the sun plays 
in producing changes in the condition of the atmospheric 
envelopes of these planets, since we should expect, if his 
action is the leading cause of changes, that the changes in 
the Jovian belts would differ°markedly in charaéter from 
those in the Saturnian belts. 
I take for granted the ordinarily described telescopic 
features of the belts, as presumably known to all the readers 
of this Journal. 
The first feature to be noticed as bearing on the condition 
of the atmospheres of Jupiter and Saturn, is the remarkable 
parallelism of the belts. It has been commonly stated that 
this feature is comparable with the existence of trade-wind 
zones on our earth. I apprehend that if our earth were 
viewed from Venus or Mercury, even with high telescopic 
power, nothing like zones would be recognised. It is, 
indeed, only over the oceans that the equatorial cloud band 
exists; and even this is but a mid-day phenomenon. The 
sun rises in a clear sky in equatorial regions at sea; and it 
is only towards noon that heavy clouds cover the whole sky. 
In the afternoon these are dissipated by heavy rain-falls and 
electric storms, and towards sunset the sky is clear. 
There is, indeed, a difficulty in accounting for the zones 
in the atmospheres of Jupiter and Saturn. Their ordinary 
regularity implies the existence of a much more effective 
cause than that which produces our trade-winds. The 
cause must be, it should seem, a difference of rotational 
velocity, causing clouds to lag as clouds on our trade zones 
do, only much more markedly, or else causing clouds to be 
carried in advance of the prevailing rotation-rate. Either 
cause would serve equally well; the difficulty lies in under 
standing how either can operate with sufficient activity. 
The rapid rotation-rates of Jupiter and Saturn would of 
course make the differences of rate correspondingly great. 
But so far as the cause which produces our own trade-winds 
is concerned, this circumstance is much more than counter- 
balanced by the greatly reduced effects of solar action in 
Jupiter and Saturn. That, notwithstanding this reduction 
of effect, sun-raised clouds should be so much more ener- 
getically swayed into zones than on our earth must be 
regarded as altogether improbable. We must find some 
other interpretation of these zones,—a result which would 
indeed have been forced upon us, as I think, by the mere 
