532 COSMOS. 



fulfilled conditions; so on the contrary the existence of satel- 

 lites accompanying the exterior planets (Jupiter, Saturn, 

 Uranus), is a phenomenon as universal as the former is rare. 

 Lassell discovered with certainty 97 the first satellite of Neptune 

 so soon as the commencement of August, 1847, in his large 

 twenty-feet reflector, with a 24 inch aperture. LasselFs dis- 

 covery was confirmed by Otto Struve 98 at Pulkowa (September 

 llth to December 20th, 1847), and Bond," the director of the 

 observatory at Cambridge (U. S.) (September 16th, 1847). 

 The Pulkowa observations gave : the period of rotation of 

 Neptune's satellite 5d. 21h. 7m. ; the inclination of its orbit to 

 the plane of the ecliptic, 34 7' ; the distance from the centre 

 of the primary, 216,000 geographical miles; the mass, 14 ^ o6 . 

 Three years afterwards (August 14th, 1850), Lassell discovered 

 a second satellite, for the examination of which he employed 

 a magnifying power of 628. 100 This last discovery has not, I 

 believe, been confirmed by other observers. 



Flemming, who will, in Dantzic, to which place he has been 

 called, continue the same reduction of observations for Saturn 

 and Jupiter which he has now made for Uranus. It is, in my 

 opinion, fortunate that he has (for the present) no means of 

 observation, and has no lectures to deliver. A time will 

 indeed come when he must institute observations with a defi- 

 nite aim; then he should no longer want the means of carrying 

 them out any more than he does the ability to do so." 



97 The first letter in which Lassell announced the discovery 

 was on the 6th of August, 1847. (Schumacher, Astr. 

 Nadir. No. 611, p. 165.) 



98 Otto Struve, in the Astr. Nadir. No. 629. August 

 Struve, in Dorpat, calculated the orbit of the first satellite of 

 Neptune from the observations at Pulkowa. 



9 W. C. Bond, in the Proceedings of the American Academy 

 of Arts and Sciences, vol. ii. pp. 137 and 140. 

 100 Schum. Astr. Nachr. No. 729, p. 143. 



