376 ANNUAL OF SCIENTIFIC DISCOVERY. 



To the supposition of a large number of small rings encircling the 

 planet, there are various objections. 



Any intervals permanently existing so large as one half, or even one 

 third, of that usually seen, could not escape observation. Moreover, 

 if the subdivisions are numerous, the width of the intervals must be 

 proportionably diminished, because the whole area occupied by them 

 goes to diminish the amount of light reflected, and to increase the 

 density of each ring, both of which are already large. The light of 

 the ring being sensibly brighter than that from an equal area on the 

 ball, it is not probable that any considerable part of the light of the 

 sun is transmitted through intervals. And to preserve the same mass, 

 if the intervals are large, the matter must be compressed, as it is not 

 allowable to give a thickness greater than is indicated by observation. 

 To avoid the hypothesis of a reflective power, and a density greater 

 than we are warranted in assuming, we must, therefore, consider the 

 intervals to be very narrow. We may take, then, the width of all but 

 the known interval as certainly less than 0.01, which is one half of 

 the width of the known interval. From the blackness of the shadow 

 of the ring upon the ball, which would be diminished in intensity were 

 a considerable part of the sun's rays transmitted, we may infer that 

 the intervals which reflect no light at all cannot occupy an area so 

 large as one fourth of the average breadth of the rings. 



It is known, in the case of a single ring, that, if it were perfectly 

 uniform in every part of its circumference, the slightest exterior dis- 

 turbance would precipitate it upon the body of the planet. To avoid this 

 catastrophe, we must suppose each ring to be an irregular solid, its 

 centre of gravity not coinciding with its centre of figure, but having a 

 motion of rotation about the body of Saturn. In addition to this, a 

 number of regular concentric rings are in a position of unstable equi- 

 librium, by virtue of their own mutual attractions. The slightest 

 inequality in the intervals would have the effect of throwing the whole 

 system into confusion. Let us suppose, for instance, that the inner 

 ring deviate, by ever so small an amount, from an exact central posi- 

 tion with reference to the ring outside it. The nearest sides commence 

 moving together, until they come in contact. All the others must 

 follow. The consequence of such a conflict of these masses, each urged 

 by different velocities, corresponding to the different times of rotation 

 of the several rings, must be fatal to the whole structure. 



It is, therefore, again necessary that the rings be not of regular 

 figure or density. But if these irregularities are small, there will be 

 only a feeble resistance opposed to their tendency to fall upon the body 

 of the planet. On the other hand, if they be large, they will become 

 the source of mutual disturbances, which must end in their destruction, 

 by causing them to fall upon each other. The sinallness of the inter- 

 vals between them, and the near equality in the period of rotation of 

 two adjacent rings, will make the danger of the latter event imminent, 

 if not wholly unavoidable. The nearness of the rings will, in any 

 case, render it impossible that they can assume a figure of equilibrium 

 permanent or nearly so. The hypothesis that the whole ring is in a 

 fluid state, or at least does not cohere strongly, presents fewer difficul- 

 ties. 



