No, 2.] BRITISH ASSOCIATION MEETING. 139 



second. Thespectrumtestof velocity applied by Lockyer showed 

 but a twentieth part of this amount as the greatest observed 

 relative velocity between different vapours in the Sun's atmos- 

 phere. 



5. NEBULiE, COMETS, AND METEORS. 



At the first Liverpool Meeting of the British Association (1854), 

 in advancing a gravitational theory to account for all the heat, 

 light, and motions of the universe, I urged that the immediately 

 antecedent condition of the matter of which the Sun and Planets 

 were formed, not being fiery, could not have been gaseous ; but 

 that it probably was solid, and may have been like the meteoric 

 stones which we still so frequently meet with through space. The 

 discovery of Huggins, that the light of the Nebulas, so far as 

 hitherto sensible to us, proceeds from incandescent hydrogen and 

 nitroo-en s-ases, and that the heads of comets also give us light of 

 incandescent gas, seems at first sight literally to fulfil that part of 

 the Nebular hypothesis to which T had objected. But a solution, 

 which seems to me in the highest degree probable, has been sug- 

 gested by Tait. He supposes that it may be by ignited gaseous 

 exhalations proceeding from the collision of meteoric stones that 

 nebulae and the heads of comets show themselves to us; and he 

 suggested, at a former meeting of the Association, that experi- 

 ments should be made for the purpose of applying spectrum 

 analysis to the light which has been observed in gunnery trials, 

 such as those at Shoeburyness, when iron strikes against iron at 

 a great velocity, but varied by substituting for the iron various 

 solid materials, metallic or stony. Hitherto this suggestion has 

 not been acted upon; but surely it is one the carrying out of 

 which ought to be promoted by the British Association. 



Most important steps have been recently made towards the 

 discovery of the natv .-e of comets ; establishing with nothing short 

 of certainty the trut^ . of a hypothesis which had long appeared 

 to me probable, — that they consist of groups of meteoric stones ; 

 accounting satisfactorily for the light of the nucleus, and giving 

 a simple and rational explanation of phenomena presented by the 

 tails of comets which had been regarded by the greatest astrono- 

 mers as almost preternaturally marvellous. The meteoric hypo- 

 thesis to which I have referred remained a mere hypothesis, (I 

 do not know that it was ever even published,) until, in ]8G(3, 

 Schiaparelli calculated, from observations on the August meteors, 

 an orbit for these bodies which he found to agree almost perfectly 



