D. Kirkwood on Satur7i^$ Rin^. 109 



Art. XVI. — Oui Saturri^s Ring ; by Daniel Kirkwood, A.M., 



Principal of Pottsv^ille Academy. 



Messrs, Editors : — I have just seen an abstract of Prof Peirce's 

 paper, " On the Constitution of Saturn'^ s Ring^'^^ read before the 

 American Association at its recent session in Cincinnati. 1 had 

 for some time doubted the truth of the generally received theory 

 of the solidity of this extraordinary girdle. To myself, therefore, 

 " the reasoning and conclusion are especially interesting. The 



lollowing remarks on the same subject are taken from a lecture 

 written a year since, and publicly delivered in the city of Read- 

 ing on the 3d of January last. Should you deem them worthy 

 of publication they are at your disposal. 



The late discovery of a remarkable harmony in the rotations 

 of the planetSj gives additional interest and importance to a vari- 

 ety of questions bearing upon the theory of the genesis of our 

 system. The rotation of Uranus — the physical constitution of 

 the Sun — the law of the planetary distances — the relative ages 

 of the planets — the rings of Saturn — all are subjects claiming the 

 earnest attention of scientific men, ^nd holding out encouraging 

 hopes of future discoveries. 



* A mistake appears. td have generally obtained with 

 respect to the epochs at which, ac(*ording to the. nebular theory, 

 the various members of our system assumed a planetary form. 

 "In this hypothesis," remarks^ Poutecoulant, "the formation of 

 the planets would not have been simultaneous ; they have been 

 created successively ai intervals of ages; the oldest are those 

 ^'hich are farthest from the Sun, and the satellites are of a more 

 recent date than tl^ir respective primaries." On the same sub- 

 ject Prof. Levering, of Cambridge, Mass., says: — "It cannot be 

 declared to be beyond the reach of the enginery of the mathe- 



d 



maticjan 



exactness 



system according to Laplace's theory, and to assign the individual 

 year when each of the outcast planets, from the gray Herschel 

 aim Saturn down to the infant Mercury, -left jts burning home 

 and became an independent orb." In regard to this question it 

 'nay be proper to remark, that the epoch of the disjunction of a 

 j;i"g from the central mass, and that of its assuming a spherical 

 torm, would be separated by an immense interval. The most 

 aistant annnlj, or those. -^rst abandoned, would require a much 

 •onger period to agglomerate aro!m(f a nucleus than those of more 

 recent origin. It is evident also that the planets having a greater 

 sphere of attraction" would require a preportionally greater 

 Jfngth of time for the process of condensation. Taking these 

 «cts into consideration, it would seem tha't the planets nearest 



