110 D. Kirkwood on Saiurn^s Ring. 



the Sun may have been the first to assume their present dimen- 

 sions. Of the major planets, Saturn has the greatest ^'sphere of 

 attraction," and hence the-duration of lis forming period must 

 likewise have been greatest. This gives rise to the interesting 

 question whether the ring of Saturn may not be the most recent 

 cosmical formation within the Hmits of the solar system, and 

 whether it may not, in the course of future ages collect about a 

 nucleus and constitute a satellite. The evidence of its soHdity 

 is not, I think, by any means conclusive. On the other hand, 

 observations made within the last few years give a degree of 

 plausibility to the presumption that it may be in a state of fluid- 

 ity, I refer to the occasional appearance of dark lines, chiefly 

 on the outer ring, which have been supposed to indicate a sub- 

 division into several concentric annuh. They do not, how- 

 ever, appear to be permanent ; at least they are subject to some 

 change, as they are not always visible, even when circumstances 

 would seem most favorable. It has also been found by delicate 

 micrometrical measurements of the rings, that they are not of 

 uniform thickness. May not this accumulation of matter on one 

 side be tiie incipient nucleus of a satellite? If so, it will be re- 

 served for future astronomers to witness a scene no less amazing 

 than the formation of a new world within the limits of the solar 

 system. 



If we admit the truth of the nebular hypothesis; it becomes an 

 interesting question whether the chaotic matter advanced with 

 regularity through all the stages of condensation, or whether its 

 contractions were sudden and violent. The former supposition 

 appears to have been generally entertained by writers on the sub- 

 ject ; but the latter, as has been observed by Prof, Nichol, seems 

 more in harmony wi^h the known operations of nature around 

 us. When gaseous substances pass to a liquid state it is not 

 generally by gradual condensation : on the other hand, such 

 changes are characterized by rapid and energetic action. The 

 same is true in most cases when a body passes from a liquid to a 

 solid state. 



It aifords me the highest gratification to know that the atten- 

 tion of some of the most distinguished mathematicians of our 

 •country has been directed to the investigation of the interesting 

 questions to which I have referred. And although in all proba- 

 bility the subject cannot be exhausted for many years — perhaps 

 for ages — the progress of research leaves little room to doubt the 

 speedy development of important results. 



Pottsville, Pa., May 19th, 1851. 



