Royal Institution. 311 



" Relinquishing, then, the idea of the visibility of th'e mere edge 

 of the ring (whether from its extreme thinness or its unreflective 

 nature), it may be asked, ' Do the appearances warrant the conclu- 

 sion, that the obscure surface is rendered visible by the reflexion to 

 us of the light reflected upon it by Saturn ? ' 



" If this were the case, might we not reasonably expect that its 

 colour would be somewhat similar to that of the obscure portion of 

 the moon as enlightened by the earth ? It is, however, of a totally 

 difi^erent hue, and strongly resembles the tarnished copper colour 

 frequently assumed by the moon under a total eclipse. May it not 

 also be fairly questioned whether the ring would be so brilliantly 

 illuminated by the reflected light of Saturn (which must fall but 

 feebly on the half of the ring furthest from the sun), as to cause 

 small portions of it to rival in brightness the satellites themselves 

 illuminated by the direct rays of the sun ; the brightest points of the 

 ring (the eastern and western extremities) receiving reflected light 

 from one half only of the illuminated surface of Saturn, which would 

 be seen from them as a half -moon ? 



" I would venture, therefore, to suggest that the illumination of 

 the obscure surface of the ring arises from the refraction of the sun's 

 light through an atmosphere surrounding each of the rings, and thus 

 throwing a pretty strong twilight upon them. During the whole 

 time that the obscure surface was turned towards the earth, the sun 

 was not more than two degrees below its plane ; and during the 

 period embraced by the observations, the depression scarcely ever 

 amounted to one degree. A very moderate density of atmosphere, 

 therefore, might suffice to produce considerable illumination of the 

 obscure surface ; much greater, probably, than the reflected light of 

 Saturn could give, and of a far ruddier tinge, more nearly resembling 

 that of our western sky shortly after sunset. 



"3. It was occasionally observed, and on Oct. 6 it is recorded, 

 that the dark shade on the ball was not uniformly black, its northern 

 portion being blacker than the southern. On three unusually fine 

 nights, viz. Oct. 26, Oct. 30, and Nov. 21, this shade was seen to 

 be divided through its whole length into two parts by an excessively 

 fine bright line. After scrutinising the object for a long time with 

 high powers, I remained perfectly convinced of the fact, which I can 

 account for only by supposing that the northern and blacker portion 

 was the shadow of the ring cast by the sun upon the ball ; that the 

 somewhat lighter shade was the ring itself seen projected upon Sa- 

 turn ; and that the bright line between the two was a portion of the 

 equatoreal regions of the planet. The relative situations of the dif- 

 ferent bodies at the time renders, I think, such an explanation pro- 

 bable." 



ROYAL INSTITUTION. 



March 15, 1850. — The Astronomer Royal *• On the present State 

 and Prospects of the Science of Terrestrial Magnetism." 



The Lecturer commenced with remarking, that the subject of his 



