ADDRESS. CI 



spiral path, mid beforo roacliing the Sim must liave been for a long time 

 exposed to an cuorinoiis heating effect from liis radiatiou when very near, 

 and must thus have been driven into vapour before aetuall}^ falling into the 

 Sun. Thus, if Mayer's hypothesis is corroyt, friction between vortices of 

 meteoric vapours and the Sun's atmosphere must be the immediate cause of 

 solar heat ; and the velocity with which these vapours circulate round equa- 

 torial parts of the Sun must amount to 435 kilometres per second. The 

 spectrum test of velocity applied by Lockyci' sliowed but a twentieth part of 

 this amount as the greatest observed relative velocity between different 

 vapours in the Sun's atmosphere. 



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

 vancing 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 nebute, so far as hitherto 

 sensible to us, proceeds from incandescent hydrogen and nitrogen gases, 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 I had 

 objected. But a solution, which seems to me in the highest degree probable, 

 has been suggested by Tait. He supposes that it may be by ignited gaseous 

 exhalations proceeding from the collision of meteoric stones that Nebnlte and 

 the heads of comets show themselves to us ; and he suggested, at a former 

 meeting of the Association, that experiments should be made for the purpose 

 of applying spectrum analysis to the light which has been observed in 

 gunnery trials, such as those at Shoeburyuess, when iron stiikes 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 pi'omoted 

 by the British Association. 



Most important steps have been recently made towards the discovery of the 

 nature of comets, establishing with nothing short of certainty the truth of a 

 h)'pothesis 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 astronomers as 

 almost preternaturally marvellous. The meteoric hypothesis to which I have 

 referred remained a mere hypothesis (I do not know that it was ever even 

 published) until, in 1866, Schiaparelli calculated, from observations on the 

 August meteors, an orbit for these bodies which he found to agree almost 

 perfectly with the orbit of the great comet of 1802 as calculated by Oppolzer ; 

 and so discovered and demonstrated that a comet consists of a group of 

 meteoric stones. Professor Xewton, of Yale College, United States, by examin- 

 ing ancient records, ascertained that in periods of about thirty-three years, 

 since the year 902, there have been exceptionally brilliant displays of the 

 November meteors. It had long been believed that these interesting visi- 

 tants came from a train of small detached planets circulating round the Sun 

 all in nearly the same orbit, and constituting a belt analogous to Saturn's 

 ring, and that the reason for the comparatively large number of meteors 

 which we observe annually about the 14th of November is, that at that 

 time the earth's orbit cuts through the supposed meteoric belt. Professor 

 Newton concluded from his investigation that there is a denser part of 



1871. h 



