262 THE NEBULAIS HYPOTHESIS. 



members of it — have as distinct a structural relation to it 

 as the planets themselves. That comets are abundant 

 round the axis of the Solar System, and grow rarer as we 

 approach its plane, implies that the genesis of comets has 

 followed some law — a law in some way concerned with the 

 genesis of the Solar System. 



If we ask for any so-called final cause of this arrange- 

 ment, none can be assigned : until a probable use for com- 

 ets has been shown, no reason can be given why they 

 should be thus distributed. But when we consider the 

 question as one of physical science, we see that comets are 

 antithetical to planets, not only in their great rarity, in 

 their motions as indifferently direct or retrograde, in their 

 eccentric orbits, and in the varied directions of those or- 

 bits ; but we see the antithesis further marked in this, that 

 while planets have some relation to the plane of nebular 

 rotation, comets have some relation to the axis of nebular 

 rotation.* And without attempting to explain the nature 

 of this relation, the mere fact that such a relation exists, 

 indicates that comets have resulted from a process of evo- 

 lution — points to a past time when the matter now forming 

 the Solar System extended to those distant regions of space 

 which comets visit. 



See, then, how differently this class of phenomena bears 

 on the antagonistic hypotheses. To the hypothesis com- 

 monly received, comets are stumbling-blocks : why there 

 should be hundreds (or probably thousands) of extremely 

 rare aeriform masses rushing to and fro round the sun, it 

 cannot say ; any more than it can explain their physical 

 constitutions, their various and eccentric movements, or 



* It is alike remarkable and suggestive, that a parallel relation exists 

 between the distribution of nebulse and the axis of our galaxy. Just aa 

 comets are abundant around the poles of our Solar System, and rare in the 

 neighbourhood of its plane : so are nebulae abundant around the poles of 

 our sidereal system, and rare in ihe neighbourhood of its plane. 



