326 SPECIAL RESULTS IN THE URANOLOGICAL 



The rotation is most rapid in the very large exterior 

 planets which have long periods of revolution, and slower 

 in the smaller planets which are nearer to the sun. The 

 period of revolution varies considerably in the asteroids, or 

 small planets between Mars and Jupiter, and will be stated 

 subsequently in the account given of each ; it is sufficient 

 at present to remark that it is longest in Hygeia and 

 shortest in Flora. 



8. Inclination of the planetary orbits and axes of 

 rotation. Next to the masses of the planets the inclina- 

 tion and excentricity of their orbits are among the most 

 important elements on which the perturbations depend. 

 Their comparison in the several series of the inner, the small 

 middle, and the outer planets (from Mercury to Mars, from 

 Flora to Hygeia, and from Jupiter to Neptune), presents 

 similarities and contrasts which lead to considerations re- 

 specting the formation of these bodies, and their secular 

 variations or changes connected with long periods of time. 

 The planets which revolve in such different elliptic orbits 

 are all situated in different planes. In order 'to render a 

 numerical comparison possible they are referred to a funda- 

 mental plane, either fixed, or moveable according to a given 

 law. It is considered most convenient to take for this 

 plane either the ecliptic (the path which the Earth really 

 passes over), or the equator of the terrestrial spheroid. 

 In addition to these planes, the subjoined table contains the 

 inclinations of the axes of rotation of the planets to their 

 own orbits, so far as these are known on the evidence of 

 tolerably secure investigation : 



