420 THE INSTABILITY OF THE HOMOGENEOUS. 



the ring would rupture at one place only; and would then 

 collapse on itself. But this is a more than questionable 

 assumption — such at least I know to be the opinion of an 

 authority second to none among those now living. So 

 vast a ring, consisting of matter having such feeble cohe- 

 sion, must break up into many parts. Nevertheless, it is 

 still inferable from the instability of the homogeneous, that 

 the ultimate result which Laplace predicted would take 

 place. For even supposing the masses of nebulous matter 

 into which such a ring separated, were so equal in their 

 sizes and distances as to attract each other with exactly 

 equal forces (which is infinitely improbable); yet the un- 

 equal action of external disturbing forces would inevitably 

 destroy their equilibrium — there would be one or more 

 points at which adjacent masses would begin to part com- 

 pany. Separation once commenced, would with ever-accel- 

 erating speed lead to a grouping of the masses. And obvi- 

 ously a like result would eventually take place with the 

 groups thus formed; until they at length aggregated into a 

 single mass. 



Leaving the region of speculative astronomy, let us con- 

 sider the Solar System as it at present exists. And here it 

 will be well, in the first place, to note a fact which may be 

 thought at variance with the foregoing argument — namely, 

 the still-continued existence of Saturn's rings; and especially 

 of the internal nebulous ring lately discovered. To the 

 objection that the outer rings maintain their equilibrium, 

 the reply is that the comparatively great cohesion of liquid 

 or solid substance would suffice to prevent any slight tend- 

 ency to rupture from taking effect. And that a nebulous 

 ring here still preserves its continuity, does not really nega- 

 tive the foregoing conclusion; since it happens under the 

 quite exceptional influence of those symmetrically disposed 

 forces which the external rings exercise on it. Here 



indeed it deserves to be noted, that though at first sight the 

 Saturn ian system appears at variance with the doctrine that 



