CELESTIAL EVOLUTION. 231 



The theory that the Sun's heat was main- 

 tained by meteors, was extended by Proctor in 

 1870 to explain the growth of the planets 

 through meteoric aggregation as well as nebular 

 condensation. Certainly the theory, as developed 

 by Proctor, accounted fairly well for the various 

 features of the Solar System ; but the highest 

 development of the meteoritic theory is due to 

 Lockyer, who published his views in 1890, in 

 his work, * The Meteoritic Hypothesis.' Lockyer 

 claims that his views are merely extensions of 

 Schiaparelli's ideas regarding the concentration 

 of celestial matter. He considered the chief 

 nebular line to be identical with the remnant 

 of the magnesium fluting, which is conspicuous 

 in cometic and meteoric spectra ; but Huggins 

 and Keeler, with more powerful instruments, 

 disproved the supposed coincidence. Lockyer 

 considers that " all self-luminous bodies in the 

 celestial space are composed either of swarms 

 of meteorites or of masses of meteoric vapour 

 produced by heat. The heat is brought about 

 by the condensation of meteor swarms, due to 

 gravity, the vapour being finally condensed into 

 a solid globe." 



Lockyer divided the stars into seven groups, 

 according to temperature, the order of evolution 

 being from red stars through a division of second- 



