148 The Planet Saturn. 



ficiently attenuated to take their place on its surface. If fluid 

 existed there in any quantity, Beer and Madler have supposed 

 that it would be raised up in a gigantic and permanent 

 equatorial tide by the attraction of the ring : of this, however, 

 there is no appearance.* Madler observes that the planet is 

 far brighter than accords with its distance from the sun (whence 

 Gruithuisen had previously inferred the existence of native 

 light) ; but this, from the analogy of Jupiter, would be due to 

 the highly reflective power of the vapours suspended in its 

 atmosphere.t The density of the ring has been valued by 

 Bessel at -j-f-g- of that of Saturn. The aspect, at least of its 

 brighter parts, is undoubtedly that of a solid, but at such a 

 distance the mere evidence of sense is fallacious — a terrestrial 

 thundercloud similarly situated would undoubtedly give as 

 bright a reflection, as hard an outline, and as black a shadow. 

 Secchi, in fact, has become convinced that the whole appendage 

 is of a gaseous nature, and consists of opaque clouds suspended 

 in an imperfectly transparent atmosphere, which renders itself 

 visible in the dusky ring, and fills up Ball's division with 

 feeble light. Theory, as has been stated, is entirely against its 

 continuous solidity. Professor Maxwell (of Aberdeen) has 

 investigated the question with great ability in an essay which 

 gained the Adams Prize at Cambridge. He has shown that 

 Laplace's result was imperfectly worked out, and that instead 

 of concluding that the rings were irregular solids of unequal 

 thickness, he should have inferred that since if solid and 

 uniform their motion would be unstable and they would be 

 destroyed, the fact that they are stable and permanent shows 

 that they are either not uniform, or not solid. He then proves 

 that so great a degree of irregularity as Laplace's theory would 

 require, being equivalent to a load upon the ring, is not con- 

 sistent with the observed structure, % and that therefore, 

 though a rigid ring is not impossible, it is impossible that the 

 rings of Saturn can be such. A continuous fluid ring would in 

 theory suffer such perturbation as to break it up ; and he 

 therefore concludes that the rings are c ' composed of an in- 

 definite number of unconnected particles, revolving round the 

 planet with different velocities according to their respective 

 distances," and that these are probably arranged in a series of 



* E. and M. thought otherwise. They interpreted in this way, curiously 

 enough, the aspect of ring C upon the ball, and imagined a corresponding deter- 

 mination of all the fluid in the ring to its inner edge, causing its more dusky 

 light. 



t 1848, Schmidt watched the gradual removal northward of the central zone, 

 ■which is usually the most luminous part, till, Sept. 17, the whole of it had passed 

 into N. latitude. 



X Schr's 100 miles, in p. 379 of our June No. being German, should have 

 stood as 460. Yet, had this been a real elevation, it seems that it would not have 

 been large enough to ensure stability. 



