594 KANSAS CITY REVIEW OF SCIENCE. 
Outside these, again, we get representations of the Calms of Cancer and Capri- 
corn, although these are not so regularly seen, the portion of the planet's surface 
polewards of the two belts being liable to great changes of appearance, some- 
times in a very short time. The portions of atmosphere representing the terres- 
trial calm-belts sometimes exhibit a beautiful rosy tint, the equatorial one espec- 
ially. The variations of this cloudy atmosphere lend great variety to the appear- 
ance of the planet at different times ; the belts are sometimes seen in large num- 
bers, and extend almost to the pole. Besides the belts, sometimes bright spots, 
sometimes dark ones, are seen, which have enabled us to determine the period 
of the planet's rotation, which, we know is very rapid — so rapid, that on the 
equator an observer would be carried round at the rate of 467 miles a minute, 
instead of seventeen as on the earth. It is easy to understand how this rapid 
rotation would break the cloud surface into belts more than with us. Although 
all astronomers do not agree that the surface of the planet is never seen, there 
are many strong reasons why it should not be seen. In the first place, Mars and 
the Earth, whose atmospheres are nearly alike, have nearly the same densities, 
while in the case of Jupiter and Saturn — the belts of which latter planet, as far 
as we can observe them, resemble Jupiter's — the density, as calculated on the 
idea that what we see is all planet, is only about one-fifth that of the Earth; and 
as the density of the Earth is five and a half times that of water, it follows that 
the densities of the the two planets in question are not far from that of water. 
Now, if we suppose that the apparent volume of Jupiter (and similarly of Saturn) 
is made up of a large shell of cloudy atmosphere and a kernel of planet, there is 
no reason why the density of the real Jupiter (and the real Saturn) should vary 
much from that of the Earth or Mars, and this would save us from a water planet 
hypothesis. Moreover, a large shell of cloudy atmosphere is precisely what our 
own planet was most probably enveloped in, in one of the early stages of its 
history. 
In addition to the changing features of this wonderful planet itself, the tele- 
scope reveals to us four moons, which as they course along rapidly in their orbits, 
and as those orbits lie nearly in the plane of the planet's orbit, lend a great addi- 
tional interest to the picture. In the various positions in their orbits the satellites 
sometimes appear at a great distance from the primary ; sometimes they come 
between us and the planet, appearing now as bright and now as dark spots on its 
surface. At other times they pass between the planet and the Sun, throwing 
their shadows on the planet's disk, and causing, in fact, eclipses of the Sun, 
They also enter into the shadow cast by the plantt, and are therefore eclipsed 
themselves, and sometimes they pass behind the planet, and are said to be oc- 
culted. Of this appearance I give below a partial table embracing only a few of 
the most notable that occur during the month ; time used is " central " or stand- 
ard : 
On the 2d at ph. 52m. 20s., Ganymede is eclipsed and reappears. 
On the 6th at gh. 41m. 57s., lo is eclipsed and reappears. 
On the 1 6th at ph, 44m. 40s., Callisto is eclipsed and disappears. 
