Work for the Telescope. 267 



enough, compared with the short existence of man, to make ns 

 anxious to see all we can of this beautiful phenomenon, whose 

 recurrence to us lies among expectations so uncertain in the 

 far-off distance. 



Were the ring symmetrical in all its parts and subdivisions, 

 as we perhaps might have expected, this description would 

 comprise all that would fall under our notice : the ellipse would 

 close up into a line, and open out into an ellipse again, with ma- 

 thematical precision. But such is not the case : there are ano- 

 malies, and like other anomalies they are, or may become, 

 peculiarly instructive. As to the knotty aspect which the ring 

 often assumes when reduced to extreme thinness, this, as 

 Gibers pointed out long ago, is the mere effect of perspective 

 foreshortening upon unequal degrees of illumination : the ring 

 consists of concentric zones of different degrees of brightness ; 

 the ends of these, when viewed very obliquely, will expose the 

 greatest amount of illuminated area, and in consequence of that 

 irradiation which apparently enlarges all luminous spaces, in 

 proportion to their brilliancy, at the expense of neighbouring 

 dark ones, will appear to project like knots or beads upon the 

 minute hue 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 reflec- 

 tion of the Star'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 ansge are unlike in 

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

 or reappearing, as in 1671, 1714, 1744, 1774, 1789, 1803, 

 1833, and 1848, we are obliged to infer some physical irregu- 

 larity; — either the rings do not all lie in the same plane, or 

 they have, as Schroter thought, mountainous prominences of 

 great magnitude : the latter idea, singular as it may appear, is 

 countenanced by the notched form of the shadow upon the ball 

 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 moveable pro- 

 tuberance in 1789 must be abandoned, at least upon that 

 ground, since his observation, never since confirmed, is contra- 

 vened by the stationary character of these projections : rotation 

 would not be incompatible with the idea of different planes; 



* This appearance I witnessed with my 5|-inch object glass on February 7 

 and 8, and March 4, last, but best under inferior definition, any obscuring cause 

 affecting the brighter less in proportion than the fainter parts of the line. 



