Stonry— Of Atmospheres upon Planets and Satellites. 323 
Hence gases with a density less than 1/10 of that of hydrogen (if any such exist) 
could escape from Jupiter. But Jupiter can prevent the escape of a gas which 
has a density a little more than a third of the density of hydrogen, and of 
all denser gases. 
Jupiter is accordingly able to imprison all gases known to chemists. His 
atmosphere may therefore, so far as can be determined by the present inquiry, 
have in it all the constituents of the Earth’s atmosphere, with the addition of 
helium and hydrogen, and any elements between hydrogen and lithium which 
the Earth may have lost; except that, if the hydrogen is sufficiently abundant, 
there can be no free oxygen. Owing to the chemical reaction that would then 
take place, the oxygen will have been used up in adding to the stock of water. 
Cuapter XI.—Of Saturn, Uranus, and Neptune. 
Our information with reference to these three planets is less satisfactory. 
Computing their radii from the data given in the Nautical Almanac, we find 
r = 61060 km. on Saturn, 
= 24700 km. on Uranus, 
= 26340 km. on Neptune. 
Their masses compared with the masses of the Earth are also sufficiently known, 
Vip8 m/M = 93°328, for Saturn, 
= 14-460, for Uranus, 
= 16°863, for Neptune ; 
but their rotation periods are very imperfectly known. We shall take them to be 
geome P = 36864 seconds, of Saturn, 
= 36000 seconds, of Uranus, 
= 36000 seconds, of Neptune. 
If we may use these values, we find 
wu = 10-412 km. /sec., on Saturn, 
4-311 km. /sec., on Uranus, 
Il 
= 4-598 km. /sec., on Neptune, 
for the velocity at the equator due to the planet’s rotation. Further, by equations 
3D2 
