310 Royal Astronomical Society. 



axis had increased. And it is still more conclusively shown by the 

 total invisibility of the ring even with Mr. Lassell's 20-foot reflector 

 on Sept. 13, when both the earth and the sun were very nearly in 

 the plane of the ring, and consequently the sun's light would be re- 

 flected from its edge with scarcely any obliquity. 



" Hence it may be inferred that the edge of the ring reflects ex- 

 tremely little light, and that the visibility of the ring, when its 

 obscure side is turned towards the earth, does not arise from the 

 sun's light reflected from the edge, but from a feeble illumination of 

 the obscure surface ; and that it is this surface only which is seen 

 and not the edge. 



" This conclusion is supported by the appearance of bright points in 

 some parts of the ring when obscurely visible : those points remain- 

 ing stationary, and not partaking of the rotation of the ring. That 

 inequalities should exist on the edge of the ring so large as to appear 

 like satellites, even with a moderate telescope, when the edge itself, 

 though directly turned towards us and fully illuminated, was quite 

 invisible with a reflector of 24 inches aperture (whose illuminating 

 power is about equal to that of an achromatic refractor of 1 7 inches 

 aperture), seems to be quite inadmissible. 



" It may be inferred, therefore, that the appearance of bright 

 points in the unilluminated ring arises from the greater reflective 

 power of some portions of its surface ; the exterior portion of the 

 inner ring being usually the largest and brightest of all, and visible 

 on both arms at equal distances from the ball. The brightness of 

 these points was not always precisely the same on each side ; at 

 some times the eastern, and at other times the western, appearing 

 the brighter. This may readily be accounted for by supposing that 

 the ring, at a given distance from its centre, may not possess the 

 same degree of reflective power throughout its whole circuit : indeed, 

 it is scarcely probable that it should ; and the observed fact is in 

 perfect harmony with the rotation of the ring, which the stationary 

 appearance of irregularities on the edge can scarcely be. 



" 2. The inquiry is interesting. Whence is the light derived which 

 renders the obscure surface of the ring visible ? 



" On this subject Sir W. Herschel says (in a paper read before 

 the Royal Society, Nov. 12, 1789), ' I may venture to say, that the 

 ring cannot possibly disappear on account of its thinness ; since, 

 either from its edge, or the sides, even if it were square on the 

 corners, it must always expose to our sight some part which is illu- 

 minated by the rays of the sun : and that this is plainly the case we 

 rnay conclude from its being visible in any telescopes during the 

 time when others of less light had lost it, and when evidently we 

 were turned towards the unenlightened side ; so that we must either 

 see the rounded part of the enlightened edge, or else the reflexion 

 of the light of Saturn upon the side of the darkened ring, as we see 

 the reflected light of the earth on the dark part of the new moon. I 

 will, however, not decide which of the two may be the case, espe- 

 cially as there are very strong reasons to induce us to think that the 

 edge of the ring is of such a nature as not to reflect much light.* 



