February ii, 19 15] 



NATURE 



645 



I have before referred to Miss Maury's c and h 

 "divisions." It is interesting- to see how the stars 

 composing them arrange themselves on the 

 ascending and descending arms. The facts are 

 g-iven in Figs. 9 and 10. 



Prof. Ejnar Hertzsprung ^° hais discussed the 

 divisions of Miss Maury's classification, and while 

 he finds that there is no systematic relationship 

 }:>etween the a and b divisions with regard to 

 spectral differences and differences of brightness, 

 vet it is otherwise in the case of the c and ac divi- 

 sions. The c stars, he finds, are very distant, and 

 are extraordinarily bright. According to him (and 

 previously according to Miss Maury) they seem 

 to suggest different physical constitutions from 

 the other divisions, and he terms them ''whales," 

 while the other stars he considers as "fishes," 

 In his paper he gives a list of twenty-four c and 

 ac stars. All of these included in my catalogue, 

 with two exceptions probably due to errors of 



XX 

 )IXX. 



. Aln/ 



ACH 



^tR xxx5<x 



PROC 



Arct 



P(SC 



Fig. to. — Position of the 

 ' 'b" stars at the top of the 

 temperature curve and on 

 the descending arm. 



classification, fall on the ascending arm of the 

 temperature curve (see Fig. 9). 



They are thus found to be condensing swarms 

 following in a natural sequence the more sparse 

 swarms so rich in variables of the o Ceti type. 



Their great luminosity is due more to volume 

 than to temperature, and the special characteristics 

 of the lines, as opposed to those of the a division, 

 are due to the difference in absorbing conditions in 

 sparse swarms and bodies with forming atmo- 

 spheres, and also to the fact that the " solar " 

 lines only occur in stars of lower temperature. 



The stars of type " h," on the other hand, are 

 seen to arrange themselves in an orderly sequence 

 following on those of type "c" (Fig. 10). At the 

 top of the ascending arm, where the sequence of 

 c stars ends, the b stars come in, and extend 

 round through the top of the curve down to the 

 Sirian stage on the descending side. This sequence 

 of the b on the c stars is a very suggestive 

 one. As a c star approaches its maximum tem- 



10 Asir. Nachrichten, vol. clxxix., No. 4296, p. 374. 

 vn oif\l VOT.. OaI 



perature, the physical conditions change from those 

 giving rise to tyjje c spectra to those from which 

 spectra of type b are produced. 



We are now in a position to derive some 

 material results from the preceding considera- 

 tions. In view of the definite manner in which 

 } the physical properties considered have shown 

 themselves to be associated with the various 

 groups on one arm of the curve or the other, we 

 are justified in using these physical properties 

 as criteria for locating stars on the ascending 

 or descending arm of the temperature curve. 



In the case of the constant bright line stars, 

 Fig. 5 shows that considerations of their physical 

 conditions may be made under the probability that 

 all these bodies are in the neighbourhood of the 

 maximum temperature attained during their evo- 

 lution. Thus the twenty-six bright line stars 

 mentioned earlier as being contained in the Har- 

 vard lists may be considered as being located on 

 the temperature curve. 



On the Harvard scheme, with the exception 

 of classes M and N, stars may belong to either, 

 as increasing and decreasing temperatures are 

 neither recognised nor provided for. In classes 

 M and X, as in my hypothesis, we are dealing 

 with the bottoms of the ascending and descending 

 branches, lowest temperatures and vastly differing 

 conditions are involved. Hence we can classify as 

 Antarian or Piscian all stars designated M or X 

 on the Harvard system. We thus obtain from 

 the Harvard Revised Photometry and the Second 

 Catalogue of \'ariable Stars, about 650 and 70 

 of these two classes respectively. 



Xext, regarding the Cepheid variables, the 

 Harvard Second Catalogue of Variable Stars con- 

 tains thirty-four short period variables with ap- 

 proximately solar spectra. These are Cepheid vari- 

 ables, and may all be placed on the ascending 

 arm, in conformity with the six already classified. 



With regard to the eclipsing variables, those 

 with continuously varying light-curves, like that 

 of & Lyrae, will probably lie on the ascending 

 arm of the temperature curve, and those like 

 Algol may be expected to occur on the descending 

 branch. 



Finallv we have to deal with the "c" and "b" 

 stars. From the manner in which the ten of 

 Miss Maury's Type "c" stars, which have been 

 classified at Kensington, aggregate on the 

 ascending arm, we may place the remaining nine 

 given in her tables " in corresponding positions. 



From the same source we find about ninet>' 

 stars of Type "b." Those classified at Kensing- 

 ton are seen to cluster round the top of the curve, 

 and to extend down the descending arm. ^ Hence, 

 when considering the physical conditions of 

 those not so classified, we may regard them as 

 occupying similar positions. 



We are thus able to add nearly 900 stars to 

 the 470 already classified on the temperature 

 basis at Kensington. ^^ 



NORM.^X LOCKVER. 



11 Annals Harv. Coll. Obs., vol. xxviii., part i. 

 K2 Catalogue of 470 of the brighter stars. 



