178 cosmos. 



et was afterward found was itself favored by the excellent 

 star-chart drawn up by Bremiker for the Berlin Academy.*" 



While among the distances of the exterior planets from the 

 Sun, that of Saturn (9-53) is nearly double as great as the 

 distance of Jupiter (5*20), the distance of Uranus (19-18) is, 

 however, more than double that of Saturn ; so the distance 

 of Neptune (30-04) is less than that which would be re- 

 quired for a repeated doubling of the distance by full ten 

 times the distance of the Earth from the Sun, i. e., an entire 

 third of Neptune's distance from the Sun. The planetary 

 boundaries were at that time 2484 million of geographical 

 miles from the central body. By the discovery of Neptune, 

 the landmark of our planetary knowledge has been advanced 

 more than 892 million miles further (more than 10 8 times 

 the distance of the Sun from the Earth). According as the 

 disturbances are recognized which each last planet expe- 

 riences, so will other planets be gradually discovered which 

 now remain invisible by means of our telescopes on account 

 of their remoteness.! 



According to the most recent determinations, Neptune's 

 period of revolution is 601267 days, or 164 years and 226 

 days, and his half major axis 30-03628. The eccentricity 

 of his orbit, next to that of Venus the smallest, is 000871946 ; 

 his mass, TT £ T F ; 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 0173.$ 



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

 was ascribed to him by Lassell and Challis. The former em- 

 ployed a magnifying power of 567, and endeavored to determ- 

 ine 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 existence of a ring 

 round Neptune. 



I dare scarcely allude in this work to the certainly earlier 

 labors of the distinguished and acute English geometrician, 



* Astr. Nackr., No. 580. 



t Leverrier, Recherches sur les Mouvemens de la Planete Herschel, 

 184G, in the Connaissance des Temps pour Van 1849, p. 254. 



\ The very important element of the mass of Neptune has been grad- 

 ually increased from ^^ according to Adams, f-gijTT according to 

 Peirce, -J* according to Bond, and T ^^ according to Sir John 

 Herschel, T3 f ^ according to Lassell, to TX faft according to Otto and 

 August Struve. The last result has been adopted in the text. 



