The Planet Saturn. 55 



accounted for on any supposition consistent with the extra- 

 ordinary flatness and thinness of the shaded body. Nor is any 

 reference made to the alternate difference of colour remarked 

 by Lassell in the two ends of the " crape veil," nor to the 

 researches of De la Rue as to the eccentricity and irregular 

 breadth of the several portions of the ring, or the deviation of 

 the dusky ring from the plane, or planes, of its neighbours. 

 Besides these omissions, a few inaccuracies might be pointed 

 out here and there ; and we should have been altogether better 

 pleased with a fuller system of reference to original authorities. 

 But we should be sorry to detract from the general merit of a 

 book in which, if the reader does not find everything which he 

 might expect from its title, he will certainly meet with much 

 that will repay the perusal, to say nothing of the very clear 

 and beautiful illustrations which accompany it ; some of which, 

 however, would have been improved by a closer following of 

 De la Rue's exquisite portraits. 



The student may probably be most struck by the hypothesis 

 which, in consequence of the researches of Mr. Maxwell (author 

 of the Cambridge Prize Essay on this subject in 1857), the writer 

 has adopted as the most plausible explanation of the structure 

 of Saturn's ring. It is composed, according to him, of a dense 

 flight of satellites, so closely grouped as to escape individual 

 recognition at our great distance, yet revolving each in its 

 separate orbit in such a manner as to secure the general per- 

 manency of the system. This idea, which is of considerable 

 antiquity, being at least as old as the time of Cassini II., is 

 much less fanciful than might be supposed by any one unac- 

 quainted with the difficulties of the subject. For though the 

 telescopic aspect of the ring produces unquestionably the im- 

 pression of continuous solidity, and this would seem to be 

 indicated by its black shadow upon the ball, yet on recognized 

 dynamical principles that condition is found to be impossible. 

 We may perhaps be excused for not assuming as confidently 

 as Mr. Proctor has done, that the period of the ring's rotation 

 is determined beyond all doubt ; our impression being rather 

 that the evidence from which it has been deduced is somewhat 

 slender ; but the fact of such a rotation seems necessarily im- 

 plied by its continuous existence under the power of gravity. 

 Whatever period, however, we assume for the rotation, it 

 cannot theoretically suit the whole breadth of the ring, each 

 appreciable portion of which would require a distinct time of 

 rotation, in proportion to its distance from the planet. And 

 hence, had it been supposed originally solid, it would have 

 been torn asunder by the strain, and broken up into an assem- 

 blage of minute concentric rings, or, as Mr. Proctor prefers to 

 think; into an immense mass of distinct satellites. 



