44 
POPULAR SCIENCE REVIEW. 
general aspect of the belts of Jupiter (Saturn is too far off for 
similar appearances to be noted) indicates the presence of 
rounded masses of cloud floating in a deep atmosphere. These 
rounded masses can only be seen as such on the middle parts 
of the disc, hut there their appearance shows unmistakably 
that they are really round, — that is, not merely round in ap- 
pearance, as a circle is round, but round as a globe is round. No 
one who has studied Jupiter with a powerful telescope can for a 
moment doubt that some at least among the cloud-masses which 
•are seen in his disc are roughly globular in shape. It is suffi- 
cient if only one of these masses has really had such a shape, 
for though any number of flat objects may float in a sea which 
so far as they were concerned might be shallow, yet if it is 
known that a single object has floated in it which was not flat, 
hut on the contrary had great length, and breadth, and thick- 
ness, we know that the sea must he a deep one. Some among 
the rounded clouds of Jupiter, which not only by their shape, 
hut by their shading, indicate a globular figure, would, if actu- 
ally globular, require an atmosphere five or six thousand miles 
deep at the very least. The atmosphere may not be so deep as 
that, or may be very much deeper. Certainly it would at once 
remove the difficulty last considered if we could suppose the 
cloud-bearing atmosphere of Jupiter to be thirteen or fourteen 
thousand miles in depth, for then the solid globe within would 
not differ very much in mean density from the globe of our 
earth. But supposing we assume, as the result of the actual 
telescopic aspect of the cloud-belts, the depth of the atmosphere to 
be but about 2000 miles, which would be less than the apparently 
minute diameter of one of the satellites, we should even then 
find that under the tremendous pressure exerted by Jupiter’s 
attraction the lower strata of such an atmosphere, if composed 
of any gases known to us, and at the temperature of our own 
air even in the torrid zones, would be simply compressed into 
the solid or liquid form. At least they could not continue to 
obey the laws which perfect gases obey under pressure. Assum- 
ing the pressure at the visible limit of the cloud envelope to be 
less than one-thousandth part of the pressure of our air at the 
sea-level, then fifteen miles below that limit the pressure would be 
equal to that of air at our sea-level, fifteen miles lower one 
thousand times as great, fifteen miles lower one million 
times as great, and fifteen miles lower yet, or still only 
sixty miles below the visible limits of the cloud envelope of 
Jupiter, the pressure would be one thousand million times 
as great as at our sea-level. The density, if only the gases 
composing that atmosphere could remain as perfect gases, would 
be more than a million times greater than the density of water, 
and thirty or forty thousand times greater than the density of 
