ASTRONOMY AND METEOROLOGY. 375 



they could scarcely have escaped detection under the scrutiny to which 

 he subjected everything appertaining to the system of Saturn for thirty 

 or forty years. Quetelet, at Paris, with an achromatic of ten inches' 

 aperture, saw the outer ring divided, in December, 1823. On the 

 17th of December, 1825, and, on the 16th and 17th of January, 1826, 

 at least three divisions were seen on the outer ring by Captain Kater. 

 At Berlin, on the 25th of April, 1837, the outer ring was seen by Prof. 

 Encke, with perfect distinctness, divided into two nearly equal parts, 

 and several divisions were recognized on the inner edge of the inner 

 ring. The great equatorial of the Berlin Observatory was used with 

 an achromatic eye-piece. On the 28th of May, the place of the outer 

 secondary interval was determined. The great optical capacity of the 

 telescope, and the eminence of Professor Encke as an observer, give the 

 highest value to these observations. On the 7th of September, 1843, 

 a division of the outer ring was detected by Messrs. Lassel and Davres, 

 at Starfield. They employed a Newtonian reflector of nine inches' 

 aperture. 



The newly discovered inner ring of Saturn cannot properly be classed 

 with the subdivisions of the old ring, as it lies within its inner edge. 



We have, then, the best assurance, in the number and reputation of 

 those who have described the phenomena in question, that to set aside 

 these appearances by referring them to some optical deception on the 

 part of the observer, or to some defect in his instrument, is an explana- 

 tion altogether insufficient and unsatisfactory. On the other hand, 

 we know that some of the best telescopes in the world, in the hands 

 of Struve, Bessel, Sir John Herschel, and others, have given no indi- 

 cation of more than one division, when the planet has appeared under 

 the most perfect definition. The fact, also, that the divisions on both 

 rings have not usually been visible together, and that the telescopes 

 which have shown distinctly several intervals in the old ring have failed 

 to reveal the new inner ring, while the latter is now seen, but not the 

 former, may be taken as some evidence that the difference is not prob- 

 ably owing to any extraordinary tranquillity or purity of the atmos- 

 phere, nor to any peculiarly favorable condition of the eye or instru- 

 ment, but rather to some real alterations in the disposition of the 

 material of the rings. Admitting this, the idea that they are in a 

 fluid state, and, within certain limits, change their form and position 

 in obedience to the laws of equilibrium of rotating bodies, naturally 

 suggests itself. There are considerations to be drawn from the state 

 of the forces acting on the rings which favor this hypothesis. For 

 instance, on the assumption that the matter of which the ring is com- 

 posed is in a solid state, we may compute, for any point on its surface, 

 the sum of the attractions of the whole ring and of Saturn. The cen- 

 trifugal force, generated by its rotation, may then be determined from 

 the condition that the particle must remain on the surface. Now, in 

 the case of a solid ring, particles on the inner and outer edges must 

 have the same period of rotation. This condition limits the breadth 

 of the ring, for, if it be found necessary for the inner and outer edges 

 to have different times of rotation, this can be accomplished only by a 

 division of the ring into two or more parts. In this way Laplace has 

 inferred the necessity of there being several rings. 



