1880.] -L5 [Kirk wood. 



March 29, aged 72, was announced by the Secretary ; and on 

 motion. Prof. Leo Lesquereaux of Columbus, 0., was ap- 

 pointed to prepare an obituary notice of the deceased. 



A short communication "On the origin of planets'' was 

 received from Prof. Daniel Kirkwood. 



Pending nominations 'Nos. 893 to 908 and new nomina- 

 tions iJ^os. 909 to 913 were read. 



On motion of Mr. J. S. Price, based upon a letter from 

 Dr. Cattell of Easton, the use of the Hall of the Society was 

 tendered to the American Philological Association for its 

 next annual meeting in July. 



And the meeting was adjourned. 



071 the Origin of Planets. By Daniel Kirkwood. 

 {Read before the American PhilosopJiical Society, April 2, 1880.) 



If Laplace's hypothesis of the formatioa of planets and satellites from 

 nebulous ringa cannot be sustained* we may conclude that each planet, at 

 its origin, was separated from a very limited arc of the equatorial pro- 

 tuberance ; or, in other words, that instead of the separation of a ring, the 

 centrifugal force produced a rupture at the point of least resistance in the 

 equatorial belt. From the chasm thus formed a nebulous mass was thrown 

 out, which in process of time was transformed into the outermost planet.f 

 The tendency to separation around the equator would thus be relieved, 

 and the ellipticity of the spheroid temporarily diminished. Further con- 

 densation, however, would again increase the centrifugal force until an- 

 other rupture or outrush similar to the first would necessarily result. The 

 formation of planets from these nebulous masses may thus be explained 

 without the necessity of supposing such matter to have been slowly col- 

 lected from continuous rings. 



The origin of satellites is also very obviously accounted for. In short, 

 where the ring hypothesis is encumbered with difficulties. well nigh insu- 

 perable, the theory here proposed seems less open to objection. Not 

 improbably, however, the ancient orbits of the secondary systems and 

 perhaps also of some of the primary planets may have differed to a con- 

 siderable extent from their present dimensions, as is shown by Mr. G. H. 

 Darwin in his " Tidal Theory of the Evolution of Satellites. ":{: 



*Proc. Amer. Phil. Soc, vol. xviii., p. 324. 



t It is now believed by astronomers that the phenomena of temporary stars, 

 such as those of 1572, 1866 and 1877, are produced bj' enormous outbursts of in- 

 candescent matter. 



JThe Observatory for July, 1879. 



