Cleveite and oilier neiv Gas Lines in the Hottest Stars. 53 



order, but that before attempting to use the unknown lines in these 

 inquiries it was important in the first instance to discriminate, if 

 possible, between gaseous and metallic lines. Until this point was 

 investigated the relative behaviour of the lines of hydrogen and 

 cleveite gases near the upper temperature limit could not be satis- 

 factorily discussed. 



The work has now been carried on a stage further, and in the 

 present paper I propose to give the results of the inquiry into (1) 

 the appearances of the lines of gases, both old and new, in the 

 spectra in question, and (2) the most probable sequence of tempera- 

 ture in the stars under discussion. 



The Spectral Lines by ivhicli the Sequence of the Hottest Stars can be 



determined. 



In the former paper I stated the sequence of certain stars, both of 

 increasing and decreasing temperature, as determined chiefly by the 

 enhanced lines of iron and the lines of the cleveite gases. At the 

 junction of the two series I provisionally grouped together Bellatrix, 

 £* Orionis, y Ursse Majoris, X Tauri, and 7 Pegasi, pointing out that 

 their spectra were not quite identical and might afterwards be 

 separated when the criteria had been further studied.* 



Further inquiry has shown that 7 Pegasi may be regarded as 

 practically identical with Bellatrix, while y Ursaa Majoris and X Tauri 

 differ from it chiefly in the general haziness of the lines ; no attempt 

 has been made, therefore, to separate these stars from Bellatrix. 

 Other stars included in the present discussion were B and e Orionis. 

 At the top of the ascending series of stars I placed Rigel and 

 £ Tauri,f and, among others, at the top of the descending series 

 were /3 Persei and a An drome da3. 



The sequence of the still hotter stars can, therefore, be deter- 

 mined by an investigation of the varying intensities in their spectra 

 of lines which appear ; also in stars on one side or other of the 

 temperature curve. The principal lines utilised in this inquiry are 

 as follows : — 



* 'Roy. Soc. Proc.,' vol. 61, p. 180. 



t This is one of the most extraordinary spectra which has been met with in the 

 Kensington series of photographs, as I have already pointed out (' Roy. Soc. Proc.,' 

 vol. 61, p. 184). While the lines of hydrogen are fairly sharp and not very broad, 

 many of the lines, especially those of the cleveite gases, are broadened almost into 

 invisibility. On the meteoritic hypothesis this is explained by the great differences 

 of velocity and direction of the meteoritic streams, the special broadening of the 

 lines of the cleveite gases indicating that these gases are chiefly concerned in dis- 

 turbances at high temperatures. 



On account of the indistinctness of many of its lines, £ Tauri is omitted from the 

 present discussion. 



