PHYSICAL ASTRONOMY. 141 
Since the time of Herschel and Schroéter, Madler in Dorpat has first, in 
our day, carefully and attentively examined the surface of Mars. It is 
moreover known that Mars alone of all the superior planets exhibits phases 
to the earth, or some slight deviation from the perfect roundness of his 
disk. 
57. The disk of the great and beautiful planet Jupiter, always appears 
with dark streaks drawn across in a determinate direction. Fig.19 givesa 
view of these streaks as observed at Slough with a 29-foot reflector on Sept. 
23, 1832 ; these are, however, by no means the same at all times. Remark- 
able dark spots also, resembling masses of clouds, are not rare; and from 
careful and continued observations of these spots, the conclusion has been 
derived, that Jupiter rotates in 9 hours, 55 minutes, 50 seconds (sidereal 
time), upon an axis perpendicular to the direction of the streaks. On 
account of the parallelism of these streaks with Jupiter’s equator, their oft- 
occurring changes, and, finally, from appearances of the spots, it may be 
maintained that these streaks belong to Jupiter’s atmosphere, forming tracts 
in a tolerably serene sky, and are produced by currents similar to our trade 
winds. They have, nevertheless, a much more permanent and decided 
character than the clouds in our atmosphere, which may result from the 
enormous velocity of rotation of the mighty planet. Moreover, that we per- 
ceive in the streaks the proportionally darker body of Jupiter is clear, from 
the well known circumstance that these streaks do not reach to the 
very edge of the disk, but fade gradually away before they arrive there. 
58. Saturn (fig. 20) is surrounded by an attendant of entirely unique and 
wonderful character; for accompanied as he is by seven moons, he is also 
surrounded by two broad and flat, though thin rings, concentric with each 
other and the planet. Both rings lie in the same plane, and are entirely 
separated from each other by a narrow, and from Saturn by a much 
broader interspace. The interval between the planet and the inner edge 
of the inner ring amounts to 16,572 geographical miles, the breadth of the 
inner ring to 29,820, the interval between the inner and the outer rings to 
1556, and the breadth of the outer ring to 18,356, and finally the thickness 
of each ring to 88 geographical miles. PI. 8, fig. 20, gives a view of Saturn 
surrounded by his rings, and with dark streaks on his surface, tolerably 
similar to those of Jupiter; they are however broader and not so evident, 
although probably originating in the same cause. The supposition that the 
double ring of Saturn is a solid and opake mass, is confirmed by the fact that 
it casts a shadow upon the planet, and is shadowed by it in certain positions 
with relation to the sun. The parallelism of the streaks with the plane of 
the ring, makes it probable that the axis of rotation of Saturn is perpendicu- 
lar to this plane, this supposition also being confirmed by the extended dark 
spots on the planet. From accurate observations of these spots, the period 
of rotation has been established at about 10 hours, 29 minutes, 177 seconds, 
59. Uranus is too distant for the observation of spots on his surface 
which might assist in determining his period of rotation. Nevertheless it 
must be supposed that like Jupiter and Saturn, Uranus possesses a very 
short term of rotation, since Madler. has plainly discovered a flattening of 
141 
