October 20, 1904] 



NA TURE 



61 



Generally, if the typical star is the brightest in the con- 

 stellation to which it belongs, the .Arabic name is used as 

 a root ; if the typical star be not the brightest, the name 

 of the constellation is used in a similar manner. Thus we 

 have Antarlan from .\ntares, Mniiamian from Alnitam, 



but when its presence is manifested by enhanced lines the 

 prefix '■ /ifo/o " is added, the idea being that a substance 

 reduced to the state in which it gives such lines is subjected 

 to some sort of molecular simplification resulting from the 

 dissociating effects of increased temperature. In the case 





K H. 



Sp t;« 



re) compared with th.it of(2)c 

 : depending upon coincidences 



nperature). The che 



Taiiriiin from (,' Tauri, Piscian from iq Piscium, and so on. 

 In this way the names given to the various groups have 

 very definite associations, and will doubtless be found 

 much more convenient than the old confusing numbers 

 and letters, even for the mere sorting of spectra into similar 

 groups. 



of hvdrogen, the proto-lines have not yet been even partially 

 produced in laboratory experiments, but that they are really 

 due to hydrogen is sufficiently demonstrated by the " series " 

 connection of their wave-lengths with the wave-lengths of 

 the more familiar lines of that element. Silicium exhibits 

 four distinct line spectra under different conditions, and it 



Fig. 4.— Stars of increasing temperature :—(i) o Oiionis (.\ntarian) ; (2) a Tauri (Aldebarian) ; (3) a Persei (Polarian); 

 U) « Cygni (Cygnian) ; (5) p Oriunis(Rigelian) ; (6) f Tauri (Taurian) ; (7) y Orionis (Crucian) ; ,8) e Orionis (AInitamian). 



Bearing in mind the important distinction to be drawn 

 between enhanced lines and the ordinary arc lines of a 

 metal, a new term was found necessary for the proper 

 chemical definition of several of the groups. When a sub- 

 stance is represented by lines which have their greatest 

 development in the arc spectrum its ordinary name suffices ; 



NO. 1825, VOL. 70] 



has been found convenient to refer to these in numbered 

 groups. It would be out of place here to reproduce all the 

 minute details of the new classification, but referring only 

 to the most characteristic lines of the various stellar groups, 

 the classification may be shortly stated as follows, the prefix 

 " p " signifying " proto " : — 



