206 



Mr. J. Norman Lockyer. 



4. The order of temperature of certain stars, as determined from 

 a comparison of the extensions of the continuous spectrum into the 

 violet or ultra-violet, is precisely the same as that which follows 

 from a comparison of the metallic spectra at the four stages of tem- 

 perature. 



5. The variations of the metallic lines furnish the most convenient 

 means of determining relative stellar temperatures, for the reason that 

 photographs with special exposures are unnecessary. 



6. Having ascertained the relative temperature of a star in this 

 way, and assuming that all the absorbing vapours are at the same 

 temperature, the presence or absence of any other metallic substance 

 can be determined by looking for the lines which are longest in its 

 spectrum at that temperature. In the case of the hottest stars, the 

 fourth stage spectrum must be the term of comparison. 



7. Accepting the new results with regard to the lines enhanced in 

 the spark, several lines in the spectra of the hottest stars, for which 

 no origins could previously be assigned, can now be ascribed to 

 metallic substances at the fourth stage of temperature. 



8. The lines of the cleveite gases appear only in the hotter stars, 

 as indicated by the extension of the continuous radiation into the 

 ultra-violet. They increase in intensity with increased temperature 

 in certain stars. 



9. The order of stellar temperatures, determined from the increas- 

 ing intensity of the lines of the cleveite gases, is identical with that 

 determined from the decreasing intensity of the metallic lines in the 

 case of those stars which show both series of lines. 



10. Different substances are spectroscopically visible through 

 different ranges of stellar temperatures. The hydrogen lines are 

 visible in stars ranging in temperature from that of cc Orionis to that 

 of Bellatrix, while those of the cleveite gases do not appear below 

 the temperature of a Cygni. The enhanced lines of calcium appear 

 at temperatures as low as a Orionis, and persist, with reduced 

 intensity, to the temperature of Bellatrix ; those of iron do not 

 appear at temperatures lower than that of cc Cygni, and disappear 

 altogether at the temperature of Bellatrix ; while the enhanced line 

 of magnesium appears at the temperature of a Cygni, and remains 

 feebly visible at the temperature of Bellatrix. 



11. It follows, then, that the enhanced metallic lines may be absent 

 from a stellar spectrum, either because the temperature is too low or 

 too high. 



12. In the case of those stars which previous investigations have 

 shown to be cooling, the metallic line phenomena are inverted. The 

 enhanced lines first become visible, then the arc lines ; while the 

 enhanced lines disappear at a certain stage in the process of cooling, 

 the arc lines continue to become stronger. 



