320 ANNUAL OF SCIENTIFIC DISCOVEEY. 



the orbit of Saturn ; if it did, it would always present its edge to the 

 sun, and neither of its sides would receive more than a horizontal 

 illumination. Nor does it lie in the plane of the orbit of the earth, 

 which is inclined to that of Saturn, and, excepting in the two points 

 where it crosses his orbit, has no reference to it whatever. But it is 

 so placed as to make a considerable angle (26 49' 17 7/ ) with the 

 orbit of Saturn, and while it is carried round the sun with the planet, 

 it remains always parallel to itself, since a fresh direction could only 

 be the result of a fresh force impressed upon it from without ; and no 

 such force exists. Hence, in the course of one revolution of Saturn, 

 or twenty-nine and a half of our years, it turns first one and then 

 the other side to the sun ; and in passing from the one to the other 

 position, presents to him for a short time its edge, in which situation, 

 from its extreme thinness, estimated by Mr. Bond at less than forty 

 miles, it will not reflect light enough to be visible at the distance of 

 the earth, without the greatest difficulty. But this is not the sole 

 condition of the phenomenon, which depends not only on the position 

 of the sun, but of the earth also ; as the earth is but seldom exactly 

 in the line between the sun and Saturn, it may so happen that the 

 edge of the ring, when not presented to the sun, may be turned 

 towards ourselves, and then again its thinness will withdraw it from 

 sight. And there is a third case of partial disappearance when the 

 sun and earth are on opposite sides of the ring, and we look on the 

 darkened side. This latter conjuncture happened during the past 

 year. 



Mr. Dawes, the English astronomer, thus describes the appearance 

 of Saturn on the 17th of May, 1862 : With a power of six hundred 

 and twenty on an eight and a half inch object-glass, the features of 

 Saturn came out with beautiful distinctness, and the edge of the disc 

 was sharply defined. The arms of the ring were scarcely at all visi- 

 ble, a very faint gleam of coppery light, at moments of finest vision, 

 being the only indication of its existence beyond the disc of the 

 planet. On the disc the projected ring appeared as a very dark line 

 a little north of the equator, and of uniform breadth. But I was 

 much surprised that, under the finest definition with this high power, 

 I could discern no trace of the shadow of the ring. I expected to see 

 it, if the atmospheric circumstances were sufficiently good, as an ex- 

 ceedingly fine black line stretched across the disc about a quarter of 

 a second to the south of the inner edge of the projected ring; and 

 that the shadow of the satellite would travel almost centrally on the 

 black line, a great part of it, however, falling on the southern portion 

 of the ring. But no such thing was to be found. Nothing, I imagine, 

 can more fully prove the almost inconceivable thinness of the ring 

 than the absence of all perceptible shadow. Had it even the least 

 thickness which has ever been ascribed to it, namely, forty miles, by 

 Mr. P. Bond, of the Harvard Observatory (United States), it would 

 be sufficient to produce a total eclipse of the sun on Saturn's equator, 

 as it would subtend an angle more than double that subtended by the 

 disc of the sun as seen from Saturn. 



A very curious phenomenon connected with the disappearance of 

 Saturn's ring is a knotty aspect which it often assumes when re- 



