192 Movements of Jupiter's Cloud-Masses . [April, 
planet like Jupiter than in that of our earth, which receives 
some twenty-seven times as much heat from the sun (mile 
for mile of surface) it is utterly incredible that precipitation 
should have occurred so steadily and swiftly along one edge 
of the great rift, and condensation — with such exactly equal 
steadiness and swiftness — on the opposite edge, that, while 
the rift as a whole shifted its position during a hundred 
Jovian nights and days at the rate of 150 miles per hour, its 
sides should nevertheless remain parallel all the time. Such 
processes may be spoken of as possible, in the same sense 
that it is possible that a coin tossed fifty times in succession 
should always show the same face ; but we do not reckon 
such possibilities among scientific contingencies. 
But the motion of great rounded masses in the atmosphere 
of Jupiter is still more decisive as to the existence not only 
of a very deep atmosphere, but also as to the swift motions 
taking place in that atmosphere. 
I would, in the first place, note that the very existence of 
belts in the Jovian atmosphere, and especially of variable 
belts, implies the great depth at which the real surface of 
the planet must lie below the visible cloud-layers. Atmo- 
spheric belts can only be formed where there are differences 
of rotational velocity. In the case of our own earth we 
know that the trade-wind zone and the counter-trade zone 
owe their origin to the difference of absolute rotational velo- 
city between the equatorial parts of the earth and parts in 
high latitudes. In the case of Jupiter the difference of this 
kind is not sufficient to account for the observed belts, — 
partly because there are many, partly because they are 
variable, but principally because Jupiter is so much larger 
than the earth that much greater distances must be traversed 
in passing from any given latitude to another where the 
rotational velocity is so many miles per hour more or less. 
Combining with these considerations the circumstance that 
the solar adtion which causes the atmospheric movements 
from one latitude to another in the case of our earth, is re- 
duced to one twenty-seventh part only of its terrestrial 
value in the case of Jupiter, we must clearly look to some 
other cause for the difference of absolute rotational velocity 
necessary to account for the belts of Jupiter. 
Now, it seems to me that we are thus at once led to the 
conclusion that the cloud-masses forming the belts of Jupiter 
are affedted by vertical currents, uprushing motions carrying 
them from regions nearer the axis, where the absolute 
motion due to rotation is slower, to regions farther from the 
axis, where the motion due to rotation is swifter, and 
