66 Mr. J. Norman Lockyer. On the Appearance of the 



these lines when at maximum are indications of a higher tempera- 

 ture than those of asterium, then, since the hydrogen and helinm 

 lines are also at a maximum, e Orionis on this assumption would be 

 the hottest star of the series. 



With our present data it is, however, difficult to state with certainty 

 whether the principal series of helium or of asterium makes its 

 appearance first. There seem, however, to be indications which 

 suggest that asterium is a somewhat later development. 



In summing up I may say that e Orionis may be considered the 

 hottest star from the behaviour of the lines at 4481-3, 4088*7, 4650-9, 

 while 4008*7, 4267'6, and 4388-1 favour the star Bellatrix in this 

 respect. 



The helium lines (4026-3 and 4471*6) have practically the same 

 intensity in both stars, or at any rate there is not sufficient difference 

 to serve as a criterion. 



General Conclusions. 



1. The order of temperature of stars at and near the apex of the 

 temperature curve can only be determined by reference to unknown 

 lines, since the enhanced lines of iron are absent, and those of mag- 

 nesium and calcium are exceedingly feeble, while the lines of the 

 known gases show no very marked variations. 



2. The varying appearances of the lines of the cleveite gases indi- 

 cate, as laboratory work has done, that helium and gas X are distinct 

 substances, but there is not yet sufficient evidence for regarding the 

 constituent series as belonging to separate substances. It is therefore 

 considered that gas X should be definitely named, and the name 

 " asterium " is suggested. 



3. There are two methods open to us for discriminating between 

 gaseous and metallic lines of still unknown origin in the spectra of 

 the hottest stars, (a) Gaseous lines like those of helium and hydro- 

 gen will be common to nebulas and the hottest stars. (6) Metallic 

 lines like those of iron, magnesium, and calcium will thin out at 

 increased stellar temperature, while gaseous lines will become inten- 

 sified. 



4. Several unknown lines in the spectra of the hottest stars are 

 thus shown to be most probably of gaseous origin. 



5. Attempts to trace terrestrial sources of these stellar gases have 

 resulted in the detection of lines which probably coincide with lines 

 in the spectra of the hottest stars. 



6. On the supposition that these stellar gases are more or less 

 allied to helium and asterium, since they have their maximum inten- 

 sity in the same stars, attempts have been made to trace " series " 

 of lines in the spectra. In the case of Bellatrix two probable series 

 have already been I'ecognised, 



