90 CELESTIAL PHENOMENA. 



true, been as yet but imperfectly investigated) exhibit some 

 remarkable differences from the movements of other satel- 

 lites and planets. In all other cases, the orbits are but 

 little inclined to the ecliptic, and the movements are from 

 west to east, including Saturn's rings, which may be regarded 

 as belts formed of an aggregation of satellites; but the 

 satellites of Uranus are almost perpendicular to the ecliptic, 

 and the direction of their movement, as confirmed by Sir 

 John Herschel from many years of observation, is retrograde, 

 or from east to west. If the primary and secondary planets 

 have been formed by condensation from annular rotating 

 portions of the primitive atmospheres of the sun and of the 

 principal planets, there must have been in the rings of va- 

 pour winch revolved round Uranus, singular and unknown 

 relations of retardation or counteraction, to have occasioned 

 the second and the fourth satellite to revolve in a direction 

 opposite to that of the rotation of the central planet. 



It appears highly probable, that the times of rotation of 

 all secondary planets, or satellites, are the same as their 

 times of revolution round their primary planets ; so that they 

 always present to the latter the same face. In the case 

 of the moon, inequalities, consequent on small variations 

 in the revolution, cause, however, fluctuations of from 

 six to eight degrees, or an apparent libration in longitude 

 as well as in latitude, which renders more than one-half 

 of her surface visible to us at different times, showing us 

 sometimes more of her western and southern limbs, and 

 sometimes more of her eastern and northern. It is this 

 libration ( 41 ) which enables us to see the annular mountain 

 of Malapert, sometimes concealed from us by the moon's 

 southern pole, the arctic landscape round the crater of 



