ISocal Institution of Q^xmt iSritatm 



WEEKLY EVENING MEETING, 



Friday, January 25, 1889. 



Colonel J. A. Grant, C.B. C.S.I. F.E.S. Vice-President, 

 in the Chair. 



Professor G. H. Darwin, M.A. LL.D. F.R.S. M.B.L 



Meteorites and the History of Stellar Systems.^ 



The great advances which have been recently made in the art of 

 celestial photography have now made it possible to study the details 

 of structure of some of the nebulae, which formerly only ap23eared as 

 a chaotic luminosity, even when viewed through a powerful telescope. 

 To illustrate this new method of research, a photograph of the great 

 nebula in Andromeda, by Mr. Isaac Eoberts, was exhibited ; it showed 

 that the nebula consists of a bright central condensation, surrounded 

 by several faintly luminous concentric rings. 



A short sketch of the Nebular Hypothesis of Laplace and Kant 

 was then given. This is a mechanical theory of the evolution of a 

 nebula into a star with attendant planets. 



It was then pointed out that Mr. Roberts's photograph exhibits 

 exactly the condition which Laplace imagined, and it thus confirms the 

 substantial truth of his hypothesis. 



But many points in the evolution of a planetary system are still 

 involved in much obscurity, and there is in particular one difficulty, 

 so fundamental that some astronomers have been led by.it virtually 

 to throw over the nebular hypothesis. 



That theory attributes the annulation of the nebula to the gradual 

 diminution and ultimate vanishing of gaseous pressure at the equator 

 of a rotating mass of gas. Thus it is the very essence of the hypo- 

 thesis that the nebula should consist of continuous gas. 



Now there is in the solar system at present no trace of the all- 

 pervading gas from which it is supposed to have been evolved, whilst 

 there is much evidence that the space surrounding the sun and 

 planets is peopled by countless loose stones or meteorites flying 

 about in various directions. 



This latter view is confirmed by the recent spectroscopic researches 

 of Mr. Lockyer, who has been led to suggest that the luminous gas, 

 which undoubtedly forms the visible portion of nebulfe, is gas vola- 

 tilised from the solid state, and rendered incandescent by violent 

 impacts between meteoric stones. These gases, he says, cool quickly, 

 cease to be luminous and condense, but the collisions being incessant, 

 the whole nebula shines with a steady light. 



* See Phil. Trans, R.S. vol. 180a (18S9). pp. 1-69. 

 Vol. XII. (No. 83.) 2 d 



