244 ON Saturn's ring. 



siderable additional increase in circumference may certainly 

 be expected, in consequence of the trees having almost 

 double the room in which to extend their branches, and for 

 the a«lmission of those powerful agents, sunshire and air. 



fTo be continued.) 



IX. 



Observations on Saturn^ s Ring : by Mr. Laplace*. 



Two con.-li- ^ ^^^^ conditions are necessary, to maintain the ring of 

 ttons necessary Saturn in eqnilibno round that planet. One respects the 

 nency ofSa " equilibriuju of its parts: v/hich requires, that the purticles 

 turn's ring. on the sxirface of the ring should not have a tendency to 

 separate from it; and that, supposing this surface to be 

 fluid, it shopld preserve itself by the different forces with 

 which it is actuated. Without this the continual effort of 

 its pj^rticles would ultimately detach them, and the ring 

 would be destroyed, like all those works of nature, which 

 have not in themselves a cause of stability able to resist the 

 action of the forces that operate against it. In the third 

 book of my Mecanique celeste I have proved, that this con- 

 dition can be fulfilled only by a rapid rotary motion of the 

 ring in its plane, and round its centre, still a little distant 

 from that of Saturn. I have likewise shown, that the sec- 

 tion of the ring by a plane perpendicular to its own, and 

 parsing through its centre, is an ellipsis elongated toward 

 this point. 

 2d condition. '^^^ second condition regards the suspension of the ring 



- ,.-. round Saturn. A hollow sphere, and generally a hollow el- 



I.oniirarent . . ^ r> j 



equil.brium of hpsoid, the inner and outer services of which were similar 



and concentric, would be in equilibrio round Saturn, what- 

 ever point of the concavity were occupied bv the centre of 

 the planet. But this equilibrium would be indifferent', 

 that is, if disturbed, it would have no tendency either to 



* Jau.na! dc Phys'^iue, vol. LXIX, n 241. 



a ho l.nv 

 sphere 



