NEPTUNE. 177 



existence of six satellites has frequently "been unjustly doubt- 

 ed ; the observations of the last twenty years have gradually 

 proved how trustworthy the great discoverer of Slough has 

 been in this as in all other branches of planetary astronomy. 

 Those satellites of Uranus which have been seen again up to 

 this time are the first, second, iourth, and sixth. Perhaps it 

 may be ventured to add the third, after the observations of 

 Lassell on the 6th of November, 1848. On account of the 

 large opening of his reflecting telescope, and the abundance 

 of hght thus obtained, the elder Herschel considered that 

 with the sharpness of his vision, under favorable atmospheric 

 circumstances, a magnifying power of 157 was sufficient ; his 

 son recommends, in general, a power of 300 for these ex- 

 tremely small luminous disks (luminous points). The second 

 and fourth satellites were seen again the earliest, the most 

 frequently and positively by Sir John Herschel, from 1828 to 

 1834, in Europe and at the Cape of Good Hope, subsequently 

 by Lament at Munich and Lassell at Liverpool. The first 

 satellite of Uranus was found by Lassell (September 14th to 

 November 9th, 1847), and by Otto Struve (October 8th to 

 December 10th, 1847). The outermost (the sixth) by La- 

 ment (October 1st, 1837). The fifth appears never to have 

 been seen again, and the third not satisfactorily enough.^ 

 The particulars here put together are not without importance, 

 also for the reason that they tend to excite caution in not 

 placing too much confidence in so-called negative evidence. 



Neptune. 



The merit of having successfully conducted and announced 

 an inverse problem of disturbance, that " of deducing from 

 the given disturbances of a known planet the elements of an 

 unknown one," and even of having, by a bold prediction, oc- 

 casioned the important discovery of Neptune by Galle on the 

 23d of September, 1846, belongs to the faculty of acute rea- 

 soning and the persevering industry of Leverrier.f This is, 

 as Encke expresses himself, the most brilliant of all planeta- 

 ry 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 plan- 



* For the observations of Lassell at Starfield (Liverpool), and of Otta 

 Struve, compare Monthly Notices of the Royal Astron. Soc, vol. viii., 

 1848, p. 43-47 and 135-139 ; also Schum., Asfr. Nachr., No. 623, p. 3fi5 



t Berhard von Liadenau, Beitrag zur Gcschichte der Neptuns-xhi:- 

 deckung, in the supplementary sheet to Schum. Astr. Nachr., ] 849, p i 



H 2 



