PHILOSOPHICAL SOCIETY OF WASHINGTON. 41 



determine small inequalities in the periodic time and motion of 

 apsides, it will be necessary to wait until the orbit is opened out 

 sufficiently to observe the satellite completely around the planet. 

 Another result of the observations is that Hyperion has a larger 

 radius vector or is moving in a larger orbit than that which is 

 due to its periodic time and Bessel's mass of Saturn. This he 

 thinks arises from the action of the large satellite Titan, whose 

 orbit is very near that of Hyperion, and the two satellites some- 

 times approach each other very closely. 



Prof. Hall remarked upon the great complexity of the Satur- 

 nian system, an 1 the relatively great perturbations to which it is 

 subject from the extreme oblateness of the planet, from the similar 

 effects of its ring, from the attractions of the satellites upon each 

 other, and from the attractions of Jupiter and the Sun, thus ren- 

 dering it a most interesting and instructive subject of contempla- 

 tion and study. 



164th Meeting. June 6, 1819. 



The President in the Chair. 

 Fifty members present.- 

 The minutes of the last meeting were read and adopted. 



The proceedings for the evening consisted in the communica- 

 tions of Messrs. C. V. Riley and Simon Kewcomb. 



The first paper by Mr. Riley was entitled — 

 pupation of the nymphalid^. 



(abstract.) 



There is no more interesting phenomenon in insect transfor- 

 mation than the withdrawal of the chrysalis from the shrunken 

 larval skin and its firm attachment to the button of silk pre- 

 viously spun by the larva, in those JRhopalocera which suspend 

 themselves perpendicularly during pupation. For a century and 

 a half Reaumur's account, namely, that the soft segments of the 

 forming chrysalis acted the part of legs by grasping the larval 

 skin between the sutures, has been accepted and generally 

 copied. Dr. J. A. Osborne, of Milford, England, first drew at- 

 tention, two yeai's ago (in Nature, vol. xvi. pp. 502-3), to the 

 fact that there was a membrane concerned in the act, and Mr. 



