PORTION OF THE COSMOS. THE PLANETS. 385 



a solidified fluid, as ice). The astronomer of Krusenstern's 

 expedition, Horner, terms the ring of Saturn a series of 

 clouds ; and would make the mountains of Saturn to consist 

 of masses and vesicles of vapour ( 628 ). Conjectural astro- 

 nomy has here a wide and legitimate field in which to exer- 

 cise itself freely. Of a wholly different kind are the severer 

 speculations, based on observation and on analytical calculus, 

 of two distinguished American astronomers, Bond and 

 Pierce, respecting the possibility of the "stability" of 

 Saturn's ring ( 629 ). They both agree in pronouncing in 

 favour of a state of fluidity, and also in favour of a continual 

 variability of form and of divisibility in the outer ring. The 

 maintenance of the general configuration is regarded by 

 Pierce as dependent on the influence and position of the 

 satellites, as without this dependence, even admitting in- 

 equalities in the ring, the equilibrium could not be preserved. 



Satellites of Saturn. 



The five oldest, or longest known, satellites of Saturn, 

 were discovered between the years 1655 and 1684 (Titan, 

 the sixth in distance, by Huygens, and four by Cassini, viz. 

 Japetus, the outermost of all, Ehea, Tethys, and Dione). 

 These discoveries were followed, in 1789, by that of the two 

 satellites nearest to the primary planet (Mimas and Ence- 

 ladus), by William Herschel. Lastly, the 7th satellite, 

 Hyperion, the last but one in point of distance, was disco- 

 vered in September, 1848, almost simultaneously, by Bond, 

 at Cambridge, U.S., and by Lassell, at Liverpool. I have 

 before treated in this work (Kosmos, Bd. i. S. 102, and 



