Cleueite and other new Gas Lines in the Hottest Stars. 



55 



3933-8 Ca(K) 

 3964-8 Gas X 

 4009-4 „ 

 4026-3 He 

 4088-7 unknown 

 4128-6 Si 

 4131-4 Si 



4173*2 unknown. 

 4179'0 unknown. 

 4340-6 Hg. 

 4267*6 unknown. 

 4388-1 Gas X. 



The accompanying map shows the sequence of spectra in the 

 hottest stars deduced from the behaviour of the above lines in passiug 

 from the stars of increasing temperature to stars of decreasing tem- 

 perature, and iucludes also some of the typical stars on both sides of 

 the curve, namely, a Cygni, >/ Leonis, and Eigel, and /3 Persei, 

 a Andromeda?, 7 Lyra?, and cc Canum Venaticorum, in the order pre- 

 viously determined. In each case the intensities of the various lines 

 are indicated by their thicknesses, so that the variations in passing 

 from star to star are plainly shown. The wave-lengths of the lines 

 and the origins of the known lines are shown at the bottom of the 

 map. 



The map enables us to discuss the relative behaviour of each of the 

 lines, and to notice which thin out or become more intense as the 

 temperature changes. 



It will be seen that when one set of lines becomes very faint or 

 disappears, another makes its appearance or becomes intensified. 



The map thus shows the most probable sequence of spectra among 

 the stars near the acme of temperature as deduced from the changes 

 of intensity of the lines given above. 



The Variations of the Cleveite Gas Lines. 



Comparison of the Principal Lines of Helium and Gas X. — In dis- 

 cussing the appearance of gas X in relation to helium, it is necessary 

 to deal with the subordinate series in each case, as the only line of 

 the principal series of helium (\ 3888*785) which falls in the photo- 

 graphic region considered coincides with a hydrogen line, and cannot 

 therefore be compared with the line of the principal series of gas X, 

 which does come within range. Taking the lines 4471*6 and 4026*3 

 as representing helium, and 4388*1 and 4009*4 as representing gas X, 

 the comparison shows that : — 



1. Gas X does not vary absolutely with helium. 



2. Gas X increases its intensity at a different rate from that of 



helium. 



3. When helium is at about a maximum so is gas X. The maxi- 



mum of gas X is, however, very short lived, while that of 

 helium extends very considerably. 



