SATURN. 521 



and irregularities, by means of which it has been possible to 

 determine approximatively their period of rotation exactly 

 the same as that of the planet. The irregularities of form 

 become perceptible on the disappearance of the rings, when 

 one is generally lost sight of before the other. 



A very remarkable phenomenon was discovered by Schwabe, 

 at Dessau, in September, 1827, the excentric position of 

 Saturn. The ring is not concentric with the planet itself, 

 but the latter is situated somewhat to the westward. This 

 observation has been confirmed partly by micrometrical mea- 

 surements by Harding, Struve, 82 John Herschel, and South. 

 The small differences in the degree of excentricity, appearing 

 periodically, which result from the corresponding observations 

 of Schwabe, Harding, and De Vico in Rome, are perhaps con- 

 sequences of oscillations of the centre of gravity of the ring 

 about the geometrical centre of Saturn. It is surprising that 

 so early as the end of the seventeenth century, a priest of 

 Avignon, named Gallet, attempted unsuccessfully to direct the 

 attention of astronomers to the excentric position of Saturn. 83 



twenty-feet reflecting telescope of his own construction. 

 Report of the British Association, 1850, p. 35. 



82 Compare Harding 's Kleine Ephemeriden for 1835, 

 p. 100; and Struve, in Schumacher's Astr. Nadir. No. 139, 

 p. 389. 



83 In the Actis Eruditorwn pro anno 1684, p. 424, is as an 

 extract from the Si/sterna Phcenomenorwrn Batumi, autore 

 Galletio, proposito eccl. Avenionensis : "Nonnunquam corpus 

 Saturni non exacte annuli medium obtinere visum fuit. Hinc 

 evenit, ut, quum planeta orientalis est, centrum ejus extre- 

 mitati orientali annuli propius videatur, et major pars ab 

 occidentali latere sit cum ampliore obscuritate." " Sometimes 

 the mass of Saturn appeared not to reach exactly the middle of 

 7iis ring. Hence it happens that when that planet is in the 

 cast his centre appears nearer to the eastern extremity of the 

 ring, and the greater part is away from the western side with 

 .greater obscurity." 



