WEI-TUNE. 27 



again up to this time are the first, second, fourth, and sixth. 

 Perhaps it may be ventured to add the third, after the obser- 

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

 the large opening of his reflecting telescope, and the abundance 

 of light thus obtained, the elder Herschel considered that 

 with the sharpness of his vision, under favourable atmospheric 

 circumstances, a magnifying power of 157 was sufficient; his 

 sou recommends in general a power of 300 for these extremely 

 small luminous discs (luminous points). The second and 

 fourth satellites were seen again the earliest, the most fre- 

 quently 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, 1 847). The outermost (the sixth) by Lament 

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

 seen again, and the third not satisfactorily enough. 91 The par- 

 ticulars 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 occa- 

 sioned the important discovery of Neptune by Galle on the 

 23rd of September, 1846, belongs to the faculty of acute 



fl For the observations of Lassell at Starfield (Liverpool), 

 and of Otto Struve, compare Monthly Notices of the Royal 

 Astrnn. Soc. vol. viii. 1818. pp. 43-47 and 135-139; also 

 Scauui. Axlr. Xaclir. No. G23, p. 365. 



