EVOLUTION A\D THEISM. 399 



extinct craters by which its surface is now made rugged, that 

 activity having been due (there can be no reasonable doubt) to 

 the rapid contraction of a solidified crust upon a still molten 

 interior. In the ring of S.iturn, on the other hand, we have a no 

 less striking exemplification, not only of the mode in \\hich the 

 detachment of the peripheral parts of the planetary masses may 

 be presumed to have given origin to their attendant satellites, 

 but of that earlier stige of condensation which consists in the 

 aggregation of nebular matter into such assemblages of small 

 solid separate masses as form the Meteor-streams with which we 

 are now familiar, and also (there is reason to believe) the trains 

 of Comets. For mathematical investigation has demonstrated 

 that the ring of Saturn, or rather the system of concentric rings, 

 cannot possibly be solid, that it is in the highest degree improb 

 able that it can be /////&amp;lt;/, whilst all the conditions of its con 

 tinuous equilibrium are satisfied by the hypothesis of its consisting 

 of streams of separate small solid masses, revolving as satellites 

 round their primary, which may itself be presumed, from the 

 specific lightness of its mass, to be still in a somewhat similar 

 stage of incipient condensation. 



Again, an entirely new series of mathematical investigations is 

 now being followed out, as to the effects at present produced by 

 tidal action in retarding the Karth s rotation, and the conclusions 

 that may be justifiably drawn from the backward projection (so 

 to speak) of that retardation, so as to apply it to an earlier stage 

 of the history of our globe and its satellite. And one of its results 

 affords so striking a confirmation of the doctrine that the existing 

 state of things is the resultant of a long sequence of previous 

 continuous change, that I shall ask your special attention to it. 

 Assuming that the Moon was once in a fluid state, the Karth s 

 attraction must have exerted a most powerful tidal influence upon 

 it ; and the retarding effect of these lunar tides would gradually 

 diminish the rate of that rotation of the Moon upon her own 

 axis, which theory would lead us to suppose that she must have 

 originally performed. At present, as every one knows, she always 

 turns the same face towards the Earth, in virtue of a rotation on 

 her axis which occupies exactly the same time as her orbital 

 revolution. Now, this phenomenon has been a standing pu/./.le 



