ASTRONOMY AND METEOROLOGY". 321 



duced to extreme thinness. This, as Olbers long ago pointed out, is 

 the mere effect of perspective foreshortening upon unequal degrees of 

 illumination. The ring consists of concentric zones of different de- 

 grees of brightness ; the ends of these, when viewed very obliquely, 

 will, in proportion to their brilliancy, appear to project like knots or 

 beads upon the minute line formed by the fainter parts of the ring. So 

 far the explanation is satisfactory ; and though these knots have been 

 seen even when the dark side of the ring has been turned towards us, 

 this has been accounted for by Bond as the reflection of the sun's light 

 from the edges of the rings,which we might see through their interstices 

 from beneath. But when we find the number of knots unequal on the 

 two sides of the planet, as has often been noticed, and especially by 

 Schroter and Harding, in 1803, or when the two ausse are unlike in 

 length, or breadth, or continuity, or in the epoch of vanishing or reap- 

 pearing, as in 1671, 1714, 1744, 1774, 1789, 1803, 1833, and 1848, we 

 are obliged to infer some physical irregularity : either the rings do not 

 all lie in the same plane, or they have, as Schroter thought, mountain- 

 ous prominences of great magnitude ; the latter idea, singular as it may 

 appear, is countenanced by the notched form of the shadow upon the 

 bail which was several times seen by him, and since by Schwabe 

 (probably) in 1848, by Lassell in 1849 and 1861, and by De La Rue 

 also last spring. If this, however, is the cause, the rotation assigned 

 to the ring by Sir W. Herschel from a movable protuberance in 

 1 789 must be abandoned, at least upon that ground, since his observa- 

 tion, never since confirmed, is contravened by the stationary charac- 

 ter of these projections. Rotation would not be incompatible with the 

 idea of different planes ; but if we may credit the statements of a far 

 inferior observer, De-Vico, who saw a lucid point adhering to the 

 opened ring in 1840 and 1842, it can no longer be maintained upon 

 any ground, and the ring must be considered fixed. How to account 

 for its stable equilibrium and permanency would then be a difficulty 

 indeed ; for even with the powerful aid of rotation it has driven the 

 American mathematicians (who have especially investigated the sub- 

 ject) from the old idea of solidity ; Pierce taking refuge in the sup- 

 position of a fluid, and Maxwell in an aggregation of unconnected 

 particles. The great Roman observer, Secchi, inclines to the idea of 

 a gaseous or vaporous constitution. The faint visibility of the dark 

 side of the ring, when it has been turned towards us, which was re- 

 marked by Herschel in 1789, and by Bond and Dawes in 1848, is 

 an additional puzzle, especially the coppery tinge which was detected 

 in it by the latter observer. It seems, from Bond's investigations, 

 that it cannot arise from a twilight produced by an atmosphere sur- 

 rounding the ring ; nor is the direction of the sun's rays favorable to 

 the idea of a slight transparency, which otherwise its astonishing 

 thinness would render very pro! table. Almost everything connected 

 with this wonderful appendage seems at present involved in impene- 

 trable mystery. 



THE APPEARANCE OF THE EARTH FROM VENUS. 



It is a curious and pleasant inquiry, what may be presumed to be 

 the telescopic aspect of our globe from the planet Venus or Mercury ; 

 and though, of course, demonstrative certainty in the reply is not 



