522 COSMOS. 



With the extremely minute density of Saturn (perhaps scarcely 

 | the density of water) and its decrease towards the surface, 

 it is difficult to form a conception of the molecular condition 

 or material constitution of the body of the planet, or even 

 to decide whether this constitution actually presupposes 

 fluidity, i. e. mobility of the smallest particles, or solidity, 

 according to the frequently adduced analogies of pine-wood, 

 pumice-stone, cork, or a solidified liquid ice. Horner, the 

 astronomer of the Krusenstern expedition, calls the ring of 

 Saturn a train of clouds ; he maintains that the mountains of 

 Saturn consist of masses of vapour.'* Conjectural astronomy 

 exercises here an unrestricted and tolerated play. Of an 

 entirely different nature are the serious speculations of two 

 distinguished American astronomers, Bond and Peirce, 

 as to the possible stability of Saturn's rings, founded upon 

 observations and the analytical calculus.** Both agree in 

 their results in favour of fluidity, as well as continuous 

 variability in the figure, and divisibility of the outer ring. 

 The permanence of the whole is considered by Peirce as 

 dependent upon the influence and position of the satellites, 

 because without this dependence, even with inequalities in 

 the ring, the equilibrium could not be maintained. 



* Horner, in Gehler's neuem physik. Worterluc7i, Bd. viii. 

 1836, p. 174. 



** Benjamin Peirce, On the Constitution of Saturn 's Ring in 

 Gould's Astron. Journal, 1851, vol. ii. p. 16. "The ring 

 consists of a stream or of streams of a fluid rather denser than 

 water flowing round the primary." Compare also Silliman's 

 A.mer. Journal, ser. ii. vol. xii. 1851, p. 99; and with regard 

 to the superficial inequalities of the ring, as well as disturbing 

 and consequently preserving influences of the satellites, Sir 

 John Herschel, Outline*, y. 320. 



