THE SATELLITES OF NEPTUNE. 



While in exterior planets the existence of a ring presents 

 itself only in one solitary instance, and its rarity permits of 

 the conjecture that the organ and formation of an unconnected 

 girdle depends upon the conjunction of peculiar and difficultly 



mical observations and astronomy. The public know no differ- 

 ence between the two ; consequently their opinion was to be 

 corrected. The indication of the development of astrono- 

 mical knowledge from observations, naturally led to the re- 

 mark that we can by no means affirm that our theory explains 

 all the motions of the planets. Uranus afforded a proof of 

 this, the old observations of which do not at all accord with 

 elements which coincide with the later observations from 1783 

 to 1820. I believe that I once told you that I have worked 

 much upon this subject, but have come to no other result 

 than the certainty that the present theory, or much rather its 

 application to the solar system, as we are acquainted with it, 

 was insufficient to solve the mystery. Nevertheless, it mu.st 

 not on that account be considered upon my opinion to be 

 unsolvable. We must first know accurately and completely 

 what has been observed of Uranus. By the aid of one of my 

 young hearers, Flemmiug, I have had all the observations re- 

 duced and compared, and thus the existing facts now lie before 

 me complete. While the old observations do not agree with the 

 theory, the more recent ones agree still less ; for now the error 

 is a whole minute, and increases annually about 7" to 8", so 

 that it will soon be much greater. I was therefore of opinion 

 that the time might come when the solution of this mystery 

 might perhaps be found in the discovery of a new planet 

 whose elements might be ascertained by its influences upon 

 Uranus, and confirmed by those exerted upon Saturn. That 

 this time has already arrived I am far from saying, but I shall 

 examine now how far the existing facts v can carry us. This is 

 an investigation which I have pursued for co many years, and 

 on account of which I have followed so many views, that its 

 results especially interest me, and shall therefore be brought 

 to an end as soon as possible. I have great confidence in 

 VOL. iv B 



