180 C0S3I0S. 



ously direcleu to the same important end, present it thni 

 laudable competition so much the more interest, as they testi- 

 fy, by the selection of means, to the present distinguished con 

 dition of high'^r mathematical knowledge. 



The Satellites of Neptune. 



While in exterior planets the existence of a ring presenti 

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

 the conjecture that the organ and formation of an unconnect- 

 ed girdle depends upon the conjunction of peculiar and diffi- 

 cultly fulfilled conditions, so, on the contrary, the existence of 

 satellites accompanying the exterior planets (Jupiter, Saturn, 

 Uranus) is a phenomenon as universal as the former is rare. 

 Lassell discovered 'vjdth certainty^ the first satellite of Nep 

 tune so soon as the commencement of August, 1847, in hi3 

 large twenty-feet reflector, with a 24-inch aperture. Las- 

 sell's discovery was confirmed by Otto Struvef at Pulkowa 



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 apphcation to the solar system, as we are acquainted 

 with it, w^as insufficient to solve the mystery. Nevertheless, it must not, 

 on that account, be considered upon my opinion to be unsolvable. We 

 must first know accui'ately and completely v^^hat has been observed of 

 Uranus. By the aid of one of my young hearers, Flemming, I have 

 had all the observations reduced 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 tha 

 time might come when the solution of this mystery might perhaps be 

 found in the discovery of a new planet whose elements might be ascer- 

 tained 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 hoio far the existing facts can carry us. This 

 is an investigation which I have pursued for so many years, and on ac- 

 count of which I have followed so many views, that its results espe- 

 cially interest me, and shall therefore be brought to an end as soon as 

 possible. I have great confidence in Flemming, who will, in Dantzic 

 to which place he has been called, continue the same reduction of ob- 

 servations for Saturn and Jupiter which he has now made for Uranus. 

 It is, in my opinion, fortunate that he has (for the present) no means 

 of observation, and has no lectures to deliver. A time will indeed come 

 when he must institute observations with a dejinite aim; then he should 

 no longer want the means of carrying them out any more than he doei 

 the ability to do so." 



*' The first letter in which Lassell announced the discovery was on 

 the 6th of August, 1847. (Schumacher, Astr. Nachr., No. 611, p. 165.) 



i Otto Struve, in the Astr. Nrrrhr., No. 62D. August Struve, in Dop 

 pat, calculated the orbit of the'first sate.lite of Neptune from the olserv 

 etioRs at Pulkowa. 



