150 ASTRONOMY FOR 1«89, 1890. 



The hist (U'teiininatiou of the thickness of kSatuin's liiifT, as Professor 

 Hall has pointed our, was made iu 1848 by W. C Bond, who found 

 that it was less than 0."01 ; Dus6jour estimated its thickness at 0."2, 

 and iSchroeter at O/'l.S. At the disappearance of the ring in Septem- 

 ber and October, 181) 1, the conditions of observation are not very 

 favorable, a better opportunity occurring in 1892. 



In connection with the approachinj»- disap])earance of the ring, an 

 account of observations made by M. E. L. Trouvelot u])on the passage 

 of the sun and earth through the plane of the rings iu 1877-'78 is of 

 especial interest. 



ISaturn's satelUies. — Dr. Hermann Struve has published the second 

 installment of his work on the theory of Saturn's satellites. In this he 

 discusses the orbits of Mimas and Enceladus, and their connection with 

 the other satellites, and he has been able to account satisfactorily for 

 the large corrections to the computed position of Mimas required 

 d:iring the past few years. In his ])revious paper Dr. Struve was led 

 to assume a sensible mass for the ring-system of Saturn, but he now 

 concludes that this hypothesis must be rejected, the mass of tlie ring 

 being so small that the terms to which it would independently give 

 rise in the disturbing function are as yet undetected by observation, 



A determination of the orbit of Titan and the mass of Saturn, the 

 result of several years' work with the Yale observatory heliometer, is 

 l)ublished by Mr. Asaph Hall, Jr., in the Transactions of the Yale 

 Observatory, 1889. His value for Saturn's mass is 1:3500.5 db 1.44, 

 agreeing well with Bessel's value 1 : 3502, and that obtained by Struve 

 1:3498. 



Uranus. — Dr. Huggins has found evidence of solar lines in the photo- 

 graphic spectrum of Uranus, with an exposure of two hours (June 3, 

 1889). All the i)riucipal solar lines were seen, but no others either 

 bright or dark. Mr. Taylor, on the other hand, has reported bright 

 flutings seen with a direct vision spectroscope attached to the five foot 

 reflecter of Common's observatory, Ealing, and if this observation is 

 confirmed it will of course prove that the planet is at least in part self- 

 luminous. 



THE MINOR PLANETS. 



The discovery of additional members of the zone of asteroids goes 

 on without the least signs of abatement, and the number has now 

 reached 301, no fewer than (J having been found in 1889, and 14 in 189i». 

 Twice during 1890 (April 25 and September 9) two were discovered on 

 the same evening by the same observer ; and the two discovered by 

 Palisa on April 25 were independently discovered by Charlois on the 

 following evening, April 26. 



