34 ME. J. H. JEANS ON THE PEAE-SHAPED EIGUEE OF EQUILIBEIUM, ETC. 
After this projectile has left the main mass, the angular momentum of the latter, 
(measured of course per unit mass) will be reduced, and as the tidal influence of the 
newly-born satellite is gradually withdrawn, the primary may settle down to a state 
of stable equilibrium in which its figure is again that of a Jacobian ellipsoid. A 
cycle of processes such as this might very conceivably constitute the life-history of a 
rotating body after once it had passed the critical state represented by the point of 
bifurcation on the Jacobian series. There seems to be no reason why the protuberance 
should always develop at, and be shot off from, the same end of the Jacobian 
ellipsoid. 
Thus it appears that the instability of the pear-shaped figure leads us to contemplate 
a series of processes of much the same nature as would have been expected if the pear 
had proved to be stable, except that we are now led to assign a much shorter time to 
these processes. The problem has ceased to be one of statics and has become one of 
dynamics; the phenomenon is no longer one of slow secular change but of collapse 
and explosion. The mechanism of planetary birth which is now suggested is so rapid 
that there need be no difficulty in supposing a planet to have been through the cycle 
several times; had the pear proved to be stable the cycle would probably have been so 
slow as to create a real difficulty. ' 
