1877-J 
Movements of Jupiter's Cloud-Masses. 
Jupiter, and but about a hundredth part on Saturn, which 
we receive from his rays. The outline of Jupiter, as indi- 
cated by the apparent position of a satellite close to his 
disc, expands and contracts through thousands of miles, yet 
the theory that Jupiter is still intensely hot must not for a 
moment be entertained, though the expansion and contrac- 
tion of the solid crust of a cool planet through so enormous 
a range would vapourise a portion of its mass exceeding 
many times the entire volume of our earth. Saturn is seen 
by Sir W. Herschel and Sir J. Herschel, by Sir G. Airy, 
Coolidge, the Bonds, and a host of other observers, to 
assume from time to time the square-shouldered aspedt, a 
change which — to be discernible from our distant standpoint 
- — would imply the expansion and contraction of whole zones 
of Saturn’s surface through 4000 or 5000 miles at least ; 
yet it is better to believe that these stupendous changes 
have affedted the solid crust of a planet like our earth, than 
to admit the possibility that the outline we measure is not 
that of the planet itself, but of layers of cloud raised to a 
vast height in the deep atmosphere surrounding a planet 
still glowing with its primeval fires. 
The phenomena I am now about to consider belong to the 
same category. They are utterly inexplicable, or only ex- 
plicable by the most sensational assumptions as to the 
processes taking place on Jupiter, if we adopt the old theory 
of Jupiter’s condition ; while if we regard Jupiter as an 
intensely-heated planet surrounded by and entirely concealed 
within a cloud-laden atmosphere several thousand miles in 
depth, they at once admit of the most simple and natural 
explanation. 
It has, of course, long been known that the belts of 
Jupiter are phenomena of his atmosphere, not of his surface. 
The belts of lightest tint have been regarded as belts of 
cloud, and the darker belts as either the real surface of the 
planet seen between the cloud-belts, or else as lower cloud- 
layers, appearing darker because in shadow. Accordingly, 
when features of the belts have been watched in their rota- 
tional circuit, it has been clearly recognised that the rotation 
determined in this way is not necessarily or probably the 
true rotation of the planet itself. Further, it has been 
proved, beyond all possibility of question, that some at least 
among the spots upon the planet’s belts have a motion of 
their own ; for whenever two spots in different Jovian lati- 
tudes have been observed, it has been almost constantly 
noticed that the one nearer the Equator has had a greater 
rotation rate than the other. Again, it has sometimes 
