ASTKOXOMY. 19 



ries in the United States, and observations were received from 

 Edgecomb at Hartford, Mitchell at Vassar College, Boss at 

 Albany, and Clark at Cambridge. It was first seen by Monck- 

 hoven, of Gand, December G, at 22 h. 15 m. sidereal time, and 

 w T as then about central. It should be noted that the rotation 

 time of Saturn'' 's ball, as given in many modern books (10 h. 

 29 m.), belongs to the ring (Laplace, " Mecanique Celeste"), 

 while the true rotation time is near that given by Sir William 

 Herschel (10 h. 16 m. 0.44 s.). Observations of this bright 

 spot on Saturn were obtained through sixty-one revolutions 

 of Saturn 's ball. The resulting rotation time is 10 h. 14 m. 

 23.8 s.2.30 s., which differs from Sir William Herschel's 

 determination (10 h. 16 m. 0.4 s.) by less than 2 m. 



Marth, of London, continues the publication of an extend- 

 ed ephemeris of the satellites of Saturn. These objects are 

 observed by Hall, of Washington, at Greenwich, by Pratt at 

 Brighton, and by Pritchett, of Glasgow, Missouri. 



Professor Hall has given in the Astronomische JVachrichten 

 elements and an ephemeris of Hyperion, the faint satellite of 

 Saturn, derived from his own observations. Although these 

 elements are regarded only as provisional, the inclination in 

 particular requiring further observations to determine it, 

 they are very close approximations, as is shown by the ac- 

 cordance of the ephemeris with the Washington observa- 

 tions of 1877. 



With regard to Hall's elements of Hyperion, Hind remarks 

 that they lead to the following numbers, assuming the solar 

 parallax as 8.86": mean distance, 914,000 miles; least dis- 

 tance, 800,000 miles; greatest distance, 1,028,000 miles. 



In Comptes Benclus (March 26), Tisserand gives the re- 

 sults of his observations of the five interior satellites of 

 Saturn. Mimas has been observed five times, Enceladus 

 seven times, etc. Tisserand gives the apparent diameter 

 of the ring, as deduced from observations of three of the 

 satellites, as below: Tethys, 40.45"; Dione, 40.61"; PJiea, 

 40.47"; mean, 40.51" which shows that the method of 

 observation adopted (William Herschel's and LasselPs) is 

 susceptible of great accuracy. 



Professor Hall read to the Philosophical Society of Wash- 

 ington a paper on the shape of the shadow of the ball of 

 Saturn on the ring, in which mention was made of the ab- 



