174 



Mr. J. Norman Lockyer. 



The Upper Limit in the case of the enhanced Metallic Lines, 



A somewhat similar difference of behaviour is noted when the 

 phenomena at the higher temperature limit are studied. The 

 enhanced lines of calcium and magnesium do not quite vanish even 

 when the temperature of Bellatrix is reached, but they become very 

 thin. With iron the case is different ; the enhanced lines vanish 

 entirely in Bellatrix, and are very much thinner than the enhanced 

 lines of calcium and magnesium in the spectrum of Rigel. 



From this it will be seen that H and K appear even at the first 

 stage of temperature, and survive up to the upper limit of Stage 4. 

 The magnesium line, 4481, does not appear until the third stage of 

 temperature is reached, but survives to the upper limit of the fourth 

 stage. In the case of iron, the enhanced lines, like that of magnesium, 

 do not appear until the third stage is reached, but, unlike it, they do 

 not survive the upper limit of the fourth stage. 



The ' Cleveite Gases. 



The lines of the cleveite gases do not appear in stellar spectra 

 until the temperature is high enough to exhibit the enhanced lines of 

 magnesium and iron with their greatest intensity. At this stage the 

 gas lines appear only very feebly, but, unlike the metallic lines, they 

 gradually increase in intensity up to the highest temperature, as 

 represented by Bellatrix. 



The range of the cleveite gas lines is therefore shorter than that of 

 the enhanced lines of iron and magnesium, and the order of intensity 

 is inverted. 



It is important to note, and I shall return to this point, that while 

 the cleveite gases are represented by absorption lines in the spectra of 

 the hotter stars only, hydrogen gives visible indications of its presence 

 in stars at nearly all stages of condensation. 



General Conclusions. 



These observations indicate individual peculiarities of the spectra 

 of the different substances. Some appear to be longer lived than 

 others, and, further, the important spectral changes in the case of 

 different substances do not occur at the same temperature 

 The differences of behaviour in the case of the enhanced 

 lines of iron, magnesium, calcium, hydrogen, and the cleveite 

 gases are illustrated diagrammatically in Map IV. It will be 

 seen from the map that there are two substances with a long range, 

 calcium and hydrogen, the former being succeeded by the latter as 

 the temperature increases ; one of intermediate range, magnesium, 

 which remains visible up to the highest temperature, and two of 



