Cleveite and other new Gas Line* in the Hottest Stars. 



65 



of hydrogen is clue most probably to a high temperature, and Pro- 

 fessor Kayser expressly states that " this series has never been 

 observed before, and can perhaps be explained by insufficient tem- 

 perature in our Geissler tubes and most of the stars."* I pointed 

 out in my former paper that this new series and the one previously 

 known are probably of the subordinate type, and that the principal 

 series is still unrecognised, f although some of the " unknown " lines 

 in stars may possibly belong to it. 



On the supposition that the new series of probable hydrogen lines 

 in £ Puppis represents the effect of a transcendental temperature, an 

 attempt has been made to produce this spectrum in the laboratory. 

 In the high-tension spark in hydrogen at atmospheric pressure the 

 ordinary series of hydrogen lines is very broad, and none of the new 

 series have so far been detected. The use of the spark with large 

 jars in vacuum tubes results in the partial fusion of the glass and the 

 appearance of lines which have been traced to silicium, while the new 

 series has not yet been observed. 



Final Result as to Temperature 



In the preliminary attempt to determine which are the hottest 

 stars, the following facts and deductions have been considered : — 



1. With increasing temperature hydrogen is first visible, then 

 helium and asterium appear nearly together, and finally unknown 

 lines at XA. 4088' 7 and 4650*9 make their appearance. 



2. The chief helium lines in the region covered by the photographs 

 become much thicker after the a Cygni stage has been passed, and 

 are practically of equal thicknesses in the stars Bellatrix, Spica, 

 o Orionis, £ Orion is, e Orionis, and ft Persei, after which a sudden 

 diminution in intensity takes place. These lines give us no critei-ion 

 for the hottest star of the series. 



3. With regard to the chief lines of asterium, namely, 40087 and 

 4388*1, in the region under investigation, these both rise to a very 

 decided maximum in Bellatrix, diminishing afterwards in intensity 

 less rapidly than they increased. The great development of asterium 

 after the lines of helium have reached a considerable thickness sug- 

 gests a higher temperature for Bellatrix than the neighbouring stars 

 in the series. . 



4. As asterium begins to decrease in intensity, the two unknown 

 lines before referred to at AA 4088*7 and 4650*9 commence to 

 brighten, reaching a maximum at e Orionis, in which the hydrogen 

 lines are still at a maximum, but asterium has considerably decreased. 

 Only a trace, if any, of these lines can be found in Bellatrix. If 



* ' Astrophysical Journal,' vol. 5, p. 96. 

 f ( Boy. Soc. Proc.,' vol. 61, p. 195. 

 VOL. LXTI. P 



