and the Theory of Saturn’s Rings. a 
These results might lead us to infer that a satellite which had 
been introduced into the region of instability by the action of a 
resisting medium, must undergo a sudden and not a gradual 
dismemberment. Before embracing this opinion, however, a few 
modifying circumstances should be considered. The change in 
the figure of the body must increase the time of rotation, while 
the diminished size of the orbit calls for a shorter period of re- 
volution ; and the synchronism of the diurnal and progressive 
movements will be destroyed. But we may safely assert that 
the effects of the resisting medium in producing this change are 
exceedingly small compared with the influence of tidal action in 
keeping the same side of the satellite always turned to its pri- 
mary, especially when the distance from the latter became very 
small. The result in such cases must be a little different for a 
solid satellite, which accommodates its form to the new conditions 
of equilibrium by a limited number of paroxysmal changes sepa- 
rated by intervals of many millions of years. On such occur- 
rences, the reduction of the velocity of rotation, together with 
the tendency of the major axis to range with the primary*, 
would lead to a series of librations, which, in a dangerous proxi- 
mity to the latter body, would tend more to promote than to 
prevent the final dismemberment. 
It must be also recollected that our formule have been deduced 
on the supposition that all parts of the satellite are equally dense ; 
and some modifications are therefore required in applying them 
to the cases likely to occur in the realms of Nature. If the den- 
sity increased very rapidly from the surface to the centre, gravity 
might be entirely suppressed at the ends of the greater axis 
before it became incapable of maintaining the stability of the 
internal matter; and it would seem that im such a case the 
satellite might part successively with many layers of the fluid of 
which it is composed, before the increased disturbance called for 
a general disunion of the internal mass. If, however, the in- 
creasing density towards the centre merely results from the great 
pressure in these localities, the separation of matter from the 
surface must weaken the tie which holds the remainder of the 
satellite together; and the dismembering action, when once 
begun, will proceed without interruption until a dissolution of 
the entire mass is completed. Butit is in cases where the satel- 
lite is solid that the mighty change im its condition assumes the 
most awful character, as the cohesion of its parts must prevent 
the gradual loss of matter from its surface, and keep the dis- 
turbing forces under restraint until they become capable of 
* There is some inaccuracy.in my last article in the incidental statement 
respecting the intensity of this directive force at different distances, 
