406 SCIENTIFIC RECORD FOR 1883. 



had become very faint, indeed barely distinguishable, in April and May, 

 and was invisible at the commencement of June, 1883. 



Professor Hough also continues his work upon this interesting phe- 

 nomenon with the Chicago 18-inch refractor. 



SATURN. 



Mass of Saturn. — In the years 1875, 1876, and 1877 Professor Hall 

 observed the difference of E. A. of Japetus and (both limbs of) Saturn 

 by means of the chronograph, measuring the difference of declination 

 also. From 128 sets of observations (20 to 25 transits in a set) the mean 

 distance of the satellite is deduced from each year separately. The 

 probable accidental error of a single year's determination of a is slightly 

 over 0".05 or toooh part. 



The resulting mean is therefore probably nearly free from accidental 

 error and is adopted by Professor Hall. It is 515".522 at Saturn's dis- 

 tance 9.53885. 



The periodic time of Japetus has been deduced by a comparison with 

 one of Sir W. Herschel's observations, those of Sir John and Washing- 

 ton observations. It is sidereal revolution =79.3310152 days. Neglect- 

 ing the action of the rings and satellites the mass of Saturn is i4 \ 2 .2- 



The Cassini division of Saturn 1 s ring. — At the January (1883) meet- 

 ing of the Eoyal Astronomical Society, Prof. J. C. Adams made a very 

 interesting communication on William Ball's observations of Saturn, 

 upon which much confusion aud misapprehension have existed. Atten- 

 tion has been directed to the subject lately by several astronomical con- 

 temporaries, mainly with the view to show that William Ball was not, 

 as he has been considered, the discoverer of the chief division of Saturn's 

 ring. Professor Adams has carefully examined letters from Ball pre- 

 served in the Archives of the Eoyal Society, Huyghen's Opera Varia, 

 etc., and remarks : " I find no evidence that Ball, any more than Huy- 

 ghens, had noticed any indication of a division in the ring." This state- 

 ment may be accepted as conclusive that the impression of several 

 English writers as to Ball's claim to the discovery of a double ring is a 

 mistaken one, and the credit of the discovery rests with Cassini. The 

 announcement of it made by the French astronomer of the Academy 

 of Sciences is in the following terms : " Apres la sortie de Saturne hors 

 des rayons du soleil l'an 1G75 dans le cr6puscule du matin, le globe de 

 cette planete parait avec une bande obscure semblable a celle de Jupi- 

 ter, 6"tendue selon la longueur de l'anneau d'orient en Occident, comme 

 elle se voit presque toujours par la lunette de 34 pieds, et la largeur de 

 l'anneau e'toit divis£e par une ligne obscure en deux parties e"gales, 

 dont l'interieur et plus proche du globe etoit fort claire, et l'inteneur 

 ud peu obscur. II y avoit entre les couleurs de ces deux parties, 

 a-peu-pres la meme difference qui est entre l'argeut mat et l'argent bruni 

 (ce qui n'avoit jamois 6t6 observe" auparavant), et ce qui s'est depuis vu 



