ASTRONOMY. 163 



ond satellite. Its albedo proves to be so high that it is capable of pre- 

 serving its brilliancy throughout the entire transit. 



The third and first satellites evidently possess sides of dift'ercnt al- 

 bedo, one high enough to maintain a brighter aspect than the other, or 

 even, as in the case of the third, to make it appear white when one side 

 is presented to the earth and dark when the other. Finally, to (]uote 

 from the original paper, " it is not unreasonable to conclude that these 

 anomalous phenomena are due to functional idiosyncrasies in the eye 

 itself, rather than to physical peculiarities of the Jovian system." 



Mr. Denning has obtained from observations of the red spot made 

 between February 12 and August 22, 1888, a rotation of 9'" 55"' 40«.21, 

 nearly one second less than the spot gave in 1885-'86, though six sec- 

 onds greater than in 1879. 



The value obtained for the mass of Jupiter by von Haerdtl in his dis- 

 cussion of Winnecke's comet is 1: 101:7.152 ± 0.013G. 



Saturn. — The first number of a new series of publications called 

 Supplements to the Pulkowa Observations contains an interesting me- 

 moir by Dr. Hermann Struve ou the outer satellites of Saturn. He dis- 

 cusses his own observations made with the 15-inch refractor in the 

 years 1884-188G on lapetus, Titan, Rhea, and Dione, with a view to 

 correcting the elements of these satellites, and also the values of tlie 

 mass and ellipticity of Saturn. The mass of Saturn wjts found by Bcs- 

 sel to be 1 : 3501. 6i 0.77, or with a slight correction indicated iu the pres- 

 ent paper, 1 : 3502.5. Prof. Asaph Hall, ou the other hand, obtained the 

 value 1 : 3481.3±0.51. Struve considers the rather large discordance be- 

 tween these values <lue to systematic error in measuring the distance 

 of a satellite from a limb, and his own observations consist entirely of 

 comi)arisons of one satellite with another, either by differences of right 

 ascension and north polar distance or of distance and position angle. 

 His resulting value of the mass of Saturn agrees closely with Bessel's, 

 being 1:3198. The correction of the elements has been carefully and 

 laboriously carried out by the method of least squares. {The Observa- 

 tory, 11 : 303, July, 1888.) 



Mr. G. W. Hill, in his i)aper on the motion of Hyperion aiul the mass 

 of Titan, has obtained for the latter 1 : 4714, Saturn's mass being unity. 

 Newcomb's corrected value, and Ormoud Stone's value, accord well with 

 this. 



Uranus. — Dr. Valentiner, of the Karlsruhe Observatory, aiul his as- 

 sistant. Dr. von Itebeur-Paschwitz, were able to detect in April, 18,S7, a 

 slight ellipticity in the disk of the planet Uranus, but their instrument, 

 a (J-inch equatorial, was not of sullicient power to make sa;tisfactory 

 measures. 



Nep'JUNE. — Tisserand has shown that the progressive changes in the 

 node and inclination of the orbit ol" the satellite of Neptunt^ can he ex- 

 plained by supposing a slight tialtening of the surface of the planet; 

 but the flattening woiihl probably be too slight to be measiired. Fur- 



