NEPTUNE. 529 



his orbit, next to that of Venus the smallest, is 0-00871946 ; 

 his mass, 1A ^ 4g ; his apparent diameter, according to Encke 

 and Galle, 2"'70, according to Challis even 3"'07; which gives 

 as his density, in comparison with the Earth, 0*230 ; greater, 

 therefore, than that of Uranus 0-173. 95 



Soon after the first discovery of Neptune by Galle, a ring 

 was ascribed to him by Lassell and Challis. The former 

 employed a magnifying power of 567, and endeavoured to 

 determine the considerable inclination of the ring to the 

 ecliptic ; but subsequent investigations have, as long before, 

 in the case of Uranus, contradicted the opinion of the exist- 

 ence of a ring round Neptune. 



I dare scarcely allude in this work to the certainly earlier 

 labours of the distinguished and acute English geometrician, 

 Mr. Adams, of St. John's College, Cambridge. The histori- 

 cal facts which refer to these labours, and to Leverrier's and 

 Galle's happy discovery of the new planet, have been circum- 

 stantially and impartially developed from reliable sources in 

 two works, by the Astronomer Royal, Airy, and by Bernhard 

 Von Lindenau. 98 Intellectual endeavours, almost simultane- 



K The very important element of the ma#s of Neptune has 

 been gradually increased from 20 | Q)7 according to Adams, 

 Tg-g^-o according to Peirce, -^gl^ according to Bond, and 

 Ts jso according to Sir John Herschel, 15 ^ 80 according to 

 Lassell, to 14 ^ 4g according to Otto and August Struve. The 

 last result has been adopted in the text. 



** Airy, in the Monthly Notices of tlie Royal Astronomical 

 Society, vol. vii. no. 9 (November, 1846), pp. 121-152. Bern- 

 hard von Lindenau, Beitrag zur Gescliichte des Neptuns- 

 Entdeckung, pp. 1-32, and 235-238. At the instigation of 

 Arago, Leverrier commenced, in the summer of 1845, his 

 investigations of the theory of Uranus. The results of this 

 investigation he laid before the Institute on the 10th of 

 November, 1845, the 1st of June, 31st of August, and 5th of 

 October, 1846, and published them at the same time ; but the 

 most extensive and important of Leverrier's labours wiiieb 



