184 SCIENTIFIC RECORD FOR 1884. 



ferent times. Professor Seeli{]fpr'.s hope is that the investigations and 

 considerations brought forward by him, in the paper before ns, may have 

 the effect of interesting photometric observers in the subject, and in- 

 ducing them to devote more attention to it than has yet been done. 

 [The Observatory, October, 1884.) 



Mass of Saturn. — From 128 observations of Japetus in 1875, 1870, and 

 1877, Prof. A. Ha?ll has determined the mean distance of this satellite 

 with a very small accidental error. The periodic time has been deter- 

 mined by a comparison with observations by the Herschels. The result- 

 ing mass of Saturn is s-i^.o- This is materially larger than the masses 

 deduced by Bessel (from Titan) and Le Verrier (from perturbations). 



The figure of the planet Uranus. — Dr. Seeliger, director of the Munich 

 Observatory, has employed the lOi-inch refractor (which has been re- 

 mounted by the Eepsolds) in measures of the disks of the various plan- 

 ets. He employs a total reflecting prism back of the eye-piece, and can 

 therefore cause any diameter of the planet to appear at any angle with 

 the vertical. 



Measures of this kind have been*made (on ten nights) on Uranus, and 

 Dr. Seeliger's result is clearly against any ellipticity of the disk. 



In this he disagrees with several late observers (Schiaparelli, Young, 

 and others), but agrees with the conclusions of Lassell, Bruhns, Engel- 

 man, and others. The question is not settled, in any event, but this 

 latest result is interesting specially on account of the method employed, 

 which avoids a dangerous kind of constant error. 



The aspect of Uranus. — At the sitting of the Academy of Sciences of 

 Paris on April 21, M. Perrotin presented a note on the aspect of Uranus, 

 from observations made with the 15-inch equatorial at the Observatory 

 of Nice. On March 18 he had remarked, in company with Mr. Lockyer, 

 a bright spot near the lower limb of the planet, as seen in the inverting 

 telescope. Further observations showed that it was near the equator 

 of Uranus. It was a very difficult object, and much uncertainty existed 

 as to its exact position; it was better seen as it approached the limb. 

 It was ol^served on April 1 about 11^', at the northern extremity of the 

 equatorial diameter, and on the next night about ICi 40™, at the south- 

 ern extremity; it occupied the same position on April 7 at 10^^30"^, and 

 April 12 at 1V\ These observations,' M. Perrotin adds, made at the 

 limits of visibility, required very favorable conditions, and being aware 

 of the possibility of illusion in such a case, he invites the attention of 

 observers possessed of powerful optical means, in order to control his 

 own impressions. The appearance and the indeterminateness in the 

 duration of the phenomenon on April 1, when the images were best, 

 rather point to a luminous belt than to a single spot, which introduces 

 uncertainty in the times of the observations; witli due regard to this, 

 M, Perrotin finds a fair agreement with the assumption of a rotation not 

 differing much from ten hours. On April 12 Mr. Trepied was present, 

 and confirmed the impressions received by the Nice ;tstronomer; he also 



