1888.] Conditions of a Swarm of Meteorites, fyc. 3 



first produced, and, if circumstances are favourable, this is further 

 oxidised to carbon dioxide. 



II. u On the Mechanical Conditions of a Swarm of Meteorites, 

 and on Theories of Cosmogony." By G. H. DARWIN, LL.D., 

 F.R.S., Fellow of Trinity College and Plumian Professor in 

 the University of Cambridge. Received July 12, 1888. 



(Abstract.) 



Mr. Lockyer writes in his interesting paper on Meteorites* as 

 follows : 



" The brighter lines in spiral nebulas, and in those in which a 

 rotation has been set up, are in all probability due to streams of 

 meteorites with irregular motions out of the main streams, in which 

 the collisions would be almost nil. It has already been suggested by 

 Professor G. Darwin (' Nature,' vol. 31, p. 25) using the gaseous 

 hypothesis that in such nebulae 'the great mass of the gas is non- 

 luminous, the luminosity being an evidence of condensation along 

 lines of low velocity according to a well-known hydrodynamical law. 

 From this point of view the visible nebula may be regarded as a 

 luminous diagram of its own stream-lines.' " 



The whole of Mr. Lockyer's paper, and especially this passage in 

 it, leads me to make a suggestion for the reconciliation of two 

 apparently divergent theories of the origin of planetary systems. 



The nebular hypothesis depends essentially on the idea that the 

 primitive nebula is a rotating mass of fluid, which at successive 

 epochs becomes unstable from excess of rotation, and sheds a ring 

 from the equatorial region. 



The researches of Rochef (apparently but little known in this 

 country) have imparted to this theory a precision which was wanting 

 in Laplace's original exposition, and have rendered the explanation of 

 the origin of the planets more perfect. 



But notwithstanding the high probability that some theory of the 

 kind is true, the acceptance of the nebular hypothesis presents great 

 difficulties. 



Sir William Thomson long ago expressed to me his opinion that 

 the most probable origin of the planets was through a gradual 

 accretion of meteoric matter, and the researches of Mr. Lockyer 

 afford actual evidence in favour of the abundancy of meteorites in 

 space. 



* 'Nature,' Nov. 17, 1887. The paper itself is in 'Roy. Soc. Pioc.,' Nov. 15, 

 1887 (No. 259, p. 117). 



f ' Montpellier, Acacl. Sci. Mem.' 



B 2 



