March i6, 1899] 



NA TURE 



465 



of stellar temperature to which the various known and 

 unknown lines, probably of gaseous origin, extend. 



Mr. McClean has stated that certain of the oxygen 

 lines (amongst which is the strong triplet at XX 407o'i, 

 4072'4 and 4076'3) appear in the spectrum of /3 Crucis 

 and other stars of nearly equal temperature. My own 

 observations, so far as they have gone, tend to confirm 

 this view ; but other photographs and more laboratory 

 work are needed to explain certain changes of intensity 

 which have been observed. The lines attributed by Mr. 

 McClean to o.xygen have been noted between a Crucis and 

 f Orionis in the upward series, and in stars at about the 

 (I Eridani stage of temperature in the downward series. 



There is evidence that the strongest lines of nitrogen 

 at X 3995'2 and X 463o'g make their appearance in stars 

 at about the temperature of n Crucis. These lines appear 

 from Rigel to f Orionis in the upward series, and are 

 present in the stars at the a Eridani stage in the downward. 



I pointed out many years ago' that at high tem- 

 peratures the fiutings of carbon in the violet are replaced 



Description of Map. 



The map is arranged on the following plan. The 

 temperature of the sun and Arcturus forms the lowest 

 stage. The upper limit is defined by y Argus, the 

 hottest star so far known. On the left the stars named 

 are those of increasing temperature, on the right those 

 of decreasing temperature. Those on the same horizon 

 represent equal mean temperatures so far as the cleveite 

 gas and enhanced lines help us to determine them. The 

 blank spaces indicate that so far no star has been photo- 

 graphed in the spectrum of which the enhanced lines 

 e.xactly match those on the opposite side. 



The names of the various chemical substances included 

 in the discussion are given at the top. I have retained 

 the prefi-x "proto" to that condition of each metallic 

 vapour which gives us the enhanced lines alone, and I 

 have added it to that form of hydrogen seen only in the 

 hottest stars. 



The behayiour of the most typical line of each 

 chemical substance is indicated by a double line looped 



3 C c <" O 



^ ■- <5 _ 



See 

 i -i ^ 





■« o o o 



^ ±: o s: 





St a S S 5 ° 



3j 10 o o 5 (n 

 i! J •^ ^ ^ <j- 



« ^ JSS 



^r — w — ^5- 



^ ♦ <T * ^ 



5! Si? Sf ?? 



by a line at X4267'5. There is a line at this wave- 

 length in the spectra of stars ranging in temperature 

 from that of Rigel to f Orionis on the up side, and from 

 a Eridani to & Persei on the down side of the temperature 

 curve. 



There is no known line of gases or metals to which 

 this line can be assigned. It is probable, therefore, that 

 carbon exists in stars of the same temperature as that at 

 which oxygen and nitrogen have been traced. 



Two lines in the spectrum of Silicium (X4i28'5 

 and X4i3f5) have been traced in stars between the 

 temperatures of a Ursas Min. and a Crucis in the upward 

 series, and between those of a Eridani and Procyon on 

 the downward. 



The accompanying map shows the facts relating to 

 stars as hot as, or hotter than, the sun, as we know them 

 at present. 



I Pnc. Key. Sec, vol. xxx. p. 461. 



NO. 1533, VOL. 59] 



at the top at its highest range. The length and varying 

 thickness of the lines in stars on both sides of the 

 temperature curve are derived from the observed appear- 

 ance and intensity of the lines, noted in the different 

 stars. 



The wave-lengths of the lines discussed are shown at 

 the bottom of the map. 



Details of Changes obseti'ed. 

 The facts embodied in the map present to us the 

 spectral changes noted in stars of Groups III., IV'. and 

 V. of my classification,' and are a result of a more 

 general inquiry than those referred to in my previous 

 papers,- the origins of a very considerable number of 

 stellar lines having since then been traced to enhanced 

 lines of metals and to known gases. 



1 Proc. Roy. Sac, vol. xliii. p. 117 (1887). 



- Proc. Roy. Soc , vol. xHv. p. i (1888) ; ibid., vol. xlv. p. 3S0 (iSSg'.); 

 Phii. Trans., 184A, 1893, p. 725. 



