528 COSMOS. 



reasoning and the persevering industry of Leverrier. 18 This is, 

 as Encke expresses himself, the most brilliant of all planetary 

 discoveries, because purely theoretical investigations have 

 rendered possible the prediction of the existence and the place 

 of the new planet. The celerity with which the planet was 

 afterwards found, was itself favoured 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 ex- 

 periences, so will other planets be gradually discovered which 

 now remain invisible by means of our telescopes on account 

 of their remoteness. 91 



According to the most recent determinations, Neptune's 

 period of revolution is 60126-7 days, or 164 years and 226 

 days, and his half major axis 30*03628. The excentricity of 



92 Berhard von Lindenau, Beitrag zur GescJiichte der 

 Nepttins-Entdeckung in the supplementary sheet to Schum. 

 Astr. Nachr. 1849. 'p. 17. 



93 Astr. Nachr. No. 580. 



94 Leverrier, Reclierclies sur les mouvemens de la Planete 

 HerscJiel, 1846, in the Connaissance des Temps pour Van 1849, 

 p. 254. 



