ASTRONOMY. 



409 



of Cassini's division, which is situated at the distance thus indicated, 

 is especially distinctly marked. The outer edge is very indistinct, the 

 influence of Ehea and Titan being much feebler on account of their 

 greater distance. 



One-fifth the period of Dione corresponds to about the distance of 

 Eucke's division. One-eighth of .Rhea's period and one-half of Titan's 

 approximate roughly to the same distance. The division is faint and 

 ill-defined. One-third the period of Tethys, the simplest relation now 

 remaining, indicates the outer boundary of the ring system, and one- 

 seventh that of Ehea and one twenty-sixth that of Titan correspond to 

 distances of nearly the same amount. 



The only simple relation omitted is that of one-fifth the period of 

 Tethys, and thus closely corresponds to integral parts of the periods of 

 the three next outer planets. There should, therefore, be another divi- 

 sion at about 14".7. Dr. Meyer does not seem aware of the fact, but 

 several observers of Saturn have noticed that ring B begins to shade off 

 a little nearer Saturn than the center of the ring, which would correspond 

 to a distance of about 14".7 or 14".8. Professor Holden speaks of the 

 point where this shading-off begins as " a definite point." The corre- 

 spondence between calculation and observation as to the divisions of 

 Saturn's rings would therefore seem to be complete. — (The Observatory, 

 September, 1833.) 



The satellites of Saturn. — Dr. W. Meyer has published (in the Astr. 

 nachr.) corrected elements of the satellites Unceladus, Tethys, Dione, 

 Ehea, Titan, and Japetus, chiefly founded upon his observations at the 

 Observatory of Geneva in 1881, the mean motions, however, being 

 determined from a comparison of the Geneva observations with the 

 elements assigned by Jacob from measures of the satellites made at 

 Madras during the years 1856-'58. The mean distances and periods 

 resulting from Dr. Meyer's investigations are as follows : 



Mean 



distance. 



Period. 



Enceladus. 

 Tethys.... 



Dione 



Ehea 



Titan 



Japetus. -. 



Radii of Sat. 



3. S661 

 4.8116 

 6. 1629 

 8. 6082 

 19.9111 

 57. 9303 



d. h. m. 



1 8 53 6.92 



1 21 18 25.62 



2 17 41 9.29 

 4 12 25 11.57 



15 22 41 23. 16 

 79 7 49 24.84 



(Nature, Aug. 16, 1883, vol. xxvm, p. 377.) 



