154 



Mr. J. N. Lockyer. 



[Nov. 17, 



VI. The brilliancy of these aggregations, at each increasing tem- 

 perature, depends on the number of meteorites in the swarm, i.e., the 

 difference depends upon the quantity, and not the intensity, of the 

 light. 



VII. The existing distinction between stars, comets, and nebulas 

 rests on no physical basis. 



VIII. The main factor in the various spectra produced is the ratio 

 of the interspaces between the meteorites to their incandescent sur- 

 face. 



IX. When the interspace is very great, the tenuity of the gases 

 given off by collisions will be so great that no luminous spectrum will 

 be produced ("nebulee " and " stars " without F bright). When the 

 interspace is less, the tenuity of the gas will be reduced, and the 

 vapours occupying the interspaces w T ill give us bright lines or flutings 

 (" nebul&e " and " stars " with F bright). When the interspace is rela- 

 tively small, and the temperature of the individual meteorites there- 

 fore higher, the preponderance of the bright lines or flutings in the 

 spectrum of the interspaces will diminish, and the incandescent 

 vapour surrounding each meteorite will indicate its presence by 

 absorbing the continuous spectrum-giving light of the meteorites 

 themselves. 



X. 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. H. Darwin* — using the gaseous hypothesis — that in such 

 nebulas "the great mass of the gas is non- luminous, the luminosity 

 being an evidence of condensation along lines of low velocity, accord- 

 ing to a well-known hydro dynamical law. From this point of view 

 the visible nebula may be regarded as a luminous diagram of its own 

 stream-lines." 



XI. New stars, whether seen in connexion with nebulas or not, are 

 produced by the clash of meteor-swarms, the bright lines seen being 

 low-temperature lines of elements the spectra of which are most 

 brilliant at a low stage of heat. 



XII. Most of the variable stars which have been observed belong 

 to those classes of bodies which I now suggest are uncondensed meteor- 

 swarms, or condensed stars in which a central more or less solid con- 

 densed mass exists. In some of those having regular periods the 

 variation would seem to be partly due to swarms of meteorites moving 

 around a bright or dark body, the maximum light occurring at peri- 

 astron. 



XIII. The spectrum of hydrogen seen in the case of the nebulas 

 seems to be due to low electrical excitation, as happens with the 



* ' Nature/ vol. 31, p. 25. 



