SATURN. 17(

a mean distance the polar diameter was 15"'38l ; the equato-
rial diameter 17"-053, consequently a flattening of'-j-i.j^.* The
hody of the planet has also ribbon-like stripes, which are, how-
ever, less perceptible, though, at the same time, rather broader
than those of Jupiter. The most constant of them is a gray
equatorial stripe. Next to this follow several others, but
with variable forms, indicating an atmospheric origin. Will-
iam Herschel did not always find them parallel to the rings,
neither do they extend as far as the poles. The region round
the poles presents a very remarkable phenomenon, a change
in the reflection of light which is dependent upon Saturn's
seasons. This region is more brightly luminous in winter, a
phenomenon which calls to mind the variable snow-region of
Mars, and did not escape the penetration of William Herschel
Whether such an increase of luminous intensity is to be asr-
cribed to the temporary formation of ice and snow, or to an
extraordinary accumulation of clouds,t it is still indicative oi
the action of changes in temperature, and of the existence ot
an atmosphere.
We have already stated the mass of Saturn to be 3 jl,- 5 ,
it, together with the enormous volume of the planet (its diam-
eter is I of the diameter of Jupiter), leads us to infer a very
small density decreasing toward the surface. If the density
were quite homogeneous (y'/^ of that of water), the flattening
would he still greater.
