ASTRONOMY. 415 



that year would probably afford a good determination of the position 

 of this plane, Professor Hall commenced a new series in March, 1881, 

 which was continued through the four oppositions to the end of May, 

 1884 ; these observations were made with magnifiers of 606 and 888 ; in 

 fair conditions of the atmosphere the outer satellites are stated to bo 

 easily observable with the Washington instrument. A comparison of 

 the measures with Professor Newcomb's tables showed that these tables 

 required but siiiall corrections, which were found by equations of con- 

 ditions in the usual manner. It should be mentioned that the tables 

 were founded mainly upon Profes<3or Neweomb's own measures ; these 

 by Professor Hall in the vear 1875 and 1876 are included in his recent 

 discussion. 



" For the position of the nodes and inclination of the orbits of the satel- 

 lites, Professor Hall finds — 



N=165O'81+0o-0142« 

 1= 75O-30-0O-0014* 



t being the number of years from 1883.0. 



" The mean value of the mass of Uranus by the observations of Oberon 

 is 22^0 31 ^^^ ^y those of Titania 22F33' ^^1 combining the values with 

 their respective weights, the final result is 22F8 2- ^^^® value, though 

 somewhat smaller than those previously obtained, Professor Hall thinks, 

 is as good as he could obtain with the filar micrometer of the large re- 

 fractor, and he does not consider that there would be much gained by a 

 continuation of the measures. He mentions that during the oppositions 

 of the planet from 1881 to 1884, which were especially favorable for the 

 search after new satellites, he made careful examination on several good 

 nights along the orbit plane of the known satellites without finding any 

 new ones. The orbits of Oberon and Titania appear to be sensibly cir- 

 cular." [Nature.) 



Neptune : The satellite of Neptune. — Appendix 11 to the Washington 

 Observations for 1881 contains Professor Hall's discussion of the obser- 

 vations of this satellite, which were made by Professor Holden and him- 

 self with the 26-inch Washington refractor: the discussion includes also 

 observations made by Lassell and Marth at Malta in 1863 and 1864. Cor- 

 rections (which come out quite small) are given for Newcomb's elements 

 of the orbit, published in Appendix i to Washington Observations for 

 1873. Comparing the observations of 1881 to 1884 with those of Lassell 

 and Marth, the periodic time is found to be 5*876839 mean solar days. 

 Lassell's period of the satellit<^, which has been adopted by Xewcomb, 

 appears to be slightly erroneous. The question of the eccentricity of 

 tjbe orbit may be more advantageously attacked some ten or twenty 

 years hence, when the apparent ellipse has become more uearlj' circular, 

 and when there will be a better opportunity to determine this element. 



