356 
POPULAK SCIENCE REYIEW. 
point properly noticed anywhere — that the seasonal changes in 
Jupiter correspond to no greater relative change than occurs 
in our daily supply of solar heat from about eight days before 
to about eight days after the spring or autumn equinox. It is 
incredible that so slight an effect as this should produce those 
amazing changes in the condition of the Jovian atmosphere 
which have unquestionably been indicated by the varying 
aspect of the equatorial zone. It is manifest that, on the one 
hand, the seasonal changes should be slow and slight so far as 
they depend on the sun, and, on the other, that the sun cannot 
rule so absolutely over the Jovian atmosphere as to cause any 
particular atmospheric condition to prevail unchanged for 
years. 
If, however, Jupiter’s whole mass is in a state of intense 
heat — if the heat is in fact sufficient, as it must be, to maintain 
an effective resistance against the tremendous force of Jovian 
gravitation — we can understand any changes, however amazing. 
We can see how enormous quantities of vapour must continually 
be generated in the lower regions to be condensed in the upper 
regions, either directly above the zone in which they were 
generated, or north or south of it, according to the prevailing 
motions in the Jovian atmosphere. And although we may not 
be able to indicate the precise reason why at one time the mid 
zone or any other belt of Jupiter’s surface should exhibit that 
whiteness which indicates the presence of clouds, and at 
another should show a colouring which appears to indicate 
that the glowing mass below is partly disclosed, we remember 
that the difficulty corresponds in character to that which is 
presented by the phenomena of solar spots. We cannot tell 
why sun-spots should wax and wane in frequency during a 
period of about eleven years ; but this does not prevent us from 
adopting such opinions as to the condition of the sun’s glowing 
photosphere as are suggested by the behaviour of the spots. 
It may be asked whether I regard the ruddy glow of Jupiter’s 
equatorial zone, during the period of disturbance lately passed 
through, as due to the inherent light of glowing matter under- 
neath his deep and cloud-laden atmosphere. This appears to 
me on the whole the most probable hypothesis, though it is 
by no means certain that the ruddy colour may not be due to 
the actual constitution of the planet’s vaporous atmosphere. 
In either case, be it noted, we should perceive in this ruddy 
light the inherent lustre of Jupiter’s glowing mass, only in 
one case we assume that that lustre is itself ruddy, in the 
other we suppose that light, originally white, shines through 
ruddy vapour-masses. It is to be remembered, however, that 
whichever view we adopt, we must assume that a considerable 
portion of the light received, even from these portions of the 
