270 THE NEBULAE HYPOTHESIS, 



broad in the line of its plane. Consequently, Saturn has a 

 rotatory movement in the same direction as the movement 

 of translation, and in a plane differing from it by thirty 

 degrees only. 



In the case of Jupiter, again, whose mass is three and a 

 half times that of Saturn, and whose orbit is little mere 

 than half the size, the genetic ring must, for the like rea- 

 sons, have been still broader — decidedly quoit-shaped, we 

 may say ; and there hence resulted a planet whose plane oi^, 

 rotation differs from that of his orbit by scarcely more than 

 three degrees. Once more, considering the comparative 

 insignificance of Mars, Earth, Venus, and Mercury, it fol- 

 lows that the diminishing circumferences of the rings not 

 sufficing to account for the smallness of the resulting 

 masses, the rings must have been slender ones — must have 

 again approximated to the hoop-shaped ; and thus it hap- 

 pens that the planes of rotation again diverge more or 

 less widely from those of the orbits. Taking into account 

 the increasing oblateness of the original sjjheroid in the 

 successive stages of its concentration, and the different 

 proportions of the detached rings, it seems to us that the 

 respective rotatory motions are not at variance with the 

 hypothesis. 



IsTot only the directions, but also the velocities of rota- 

 tion are thus explicable. It might naturally be supposed 

 that the large planets would revolve on their axes more 

 slowly than the small ones : our terrestrial experiences in- 

 cline us to expect this. It is a corollary from the Nebular 

 Hypothesis, however, more especially when interpreted as 

 above, that while large planets will rotate rapidly, small 

 ones will rotate slowly ; and we find that in fact they do 

 BO. Other things equal, a concentrating nebulous mass 

 that is diffused through a wide space, and whose outer parts 

 have, therefore, to travel from great distances to the com- 

 mon centre of gravity, will acquire a high axial velocity in 



