ASTRONOMY. 407 



toujours par la meme lunette, niais plus clairement dans la erepuscuel 

 et a la clarte - cle la lune que dans une nuit plus obscure. Cette appar- 

 ency donna une idde comme d'un anneau double, dont l'inferieur plus 

 lar: e et plus obscur fiit charge d'un plus etroit et plus clair." In two 

 figures attached to this announcement the ring is shown with the outer 

 half shaded and the inner half white, and there is a central band across 

 the globe. — (Nature.) 



Rings of Saturn. — Mr. William B. Taylor recalls attention to the an- 

 nouncement made by Otto Struve in 1851, that the observations of two 

 hundred years showed the rings of Saturn to be widening, and the 

 inner edge of the inner bright ring to be approaching the body of the 

 planet. 



"Accepting the only tenable theory of the rings, that they are com- 

 posed of discrete particles, each revolviug in its own orbit, we may, by 

 Kepler's law, compute the period of rotation of any part of the riug. 

 Assuming the period of the inner satellite (Mimas) to be 22h. 37£in., 

 the computed period of the outer edge of the ring is 14h. 30m ; of the 

 dividing stripe, llh. 20m. ; of the inner edge of the bright ring, 7h. 

 12m. ; of the inner edge of the dusky ring, 5h. 45m. ; and of the ring- 

 as a whole (supposed solid), about lOh. 50m. The period of the planet 

 is lOh. 14m. 



" With the complex perturbations induced by the exterior satellites, it 

 is evident that no particle of the ring can revolve in a circular orbit ; 

 and it follows that, in a space so crowded with particles as to give a 

 continuous light, there must be much interference. Whether the col- 

 lisions at intercepting orbits result in heat or in disintegration, they 

 necessarily tend to a degradation of motion, and hence to a shortening 

 mean radius-vector and a diminishing period. 



"It thus appears that Struve's conclusions have a rational theoretic 

 basis. The rings are falling toward the planet and will eventually be 

 absorbed. Indeed, on the generally received meteoric theory of their 

 constitution, it is impossible to regard their present condition other- 

 wise than as an evanescent phase of a progressive evolution." 



Mr. Taylor points out that the relation between the rotation periods 

 of the planet and the ring, and the relation between the rotation periods 

 of Mars and its satellites, not only fail to impeach the nebular hypoth- 

 esis, as some have supposed, but even fail to be anomalous. 



If the planet had a velocity of rotation equal t*o that of a satellite re- 

 volving at its surface, it could not approach the spherical shape. And, 

 the form having once been assumed, the rate of rotation must neces- 

 sarily and continuously diminish through the influence of solar tides, 

 until eventually the planetary day and year are identical. — (Phil. Soc. 

 Washington ; meeting October 13, 1883.) 



The divisions in Saturn's rings.* — Professor Kirkwood showed some 



Astron. Nachr., No. 2527. 



