418 



Mr. J. N. Lockyer. On the Cause of [Nov. 21, 



The remaining stars observed by Duner are not included in the 

 classification at present, owing to insufficient details. 



The result of this comparison of Duner's and Chandler's observa- 

 tions, taken in conjunction with my classification in species of the 

 bodies of Group II, goes to show that the swarms with a mean con- 

 densation are the reddest. For, although the results are not quite so 

 uniform as might be desired, there is a decided maximum of redness 

 in species 9 and 10, which may fairly be taken as the swarms with 

 mean spacing. The greatest discrepancy is in Species 1, but here the 

 result depends upon the observations of one star, and even that is not 

 definitely known to belong to Species 1. (See "Bakerian Lecture," 

 P- 65.) ' 



It may be objected that the foregoing series of numbers is not 

 sufficiently regular for any trustworthy conclusions to be arrived at. 

 But the very decided maximum in Species 10 is of itself sufficient 

 evidence that the irregularities on both sides of it are due to the 

 difficulties of observation. I have gone over Duner's observations of 

 the spectra and colours of the bodies of Group II without reference to 

 my temperature classification, and the result shows that where the 

 spectra are described as ideutical, the colours sometimes differ con- 

 siderably. The table on page 419 shows that this is the case. The 

 numbers in the vertical columns indicate the numbers of stars of any 

 particular colour associated with a particular spectrum. Thus, 

 amongst the stars with a spectrum containing the band 1 — 10 

 uniformly developed, 3 have the colour Rrj, and 5 are Rj. 



It will be seen, therefore, that, even if my classification into species 

 be not accepted, the relation between colour and spectrum in the 

 present state of our knowledge is not absolutely definite. 



[This is probably to a great extent due to the variability of the 

 stars of the group. All of them may be more or less variable, and it 

 may often have happened that the colour of a star has been recorded 

 at one time and its spectrum at another, when the colour was slightly 

 different. Some of the slight variations observed may also be due 

 to variation in the atmospheric absorption. — November 1, 1889.] 



On reference to the tables of variables which I give in this paper it 

 will be seen also that the relation between colour and period observed 

 by Chandler is only a general one. 



We may, therefore, for the present regard the swarms with mean 

 spacing as the reddest. The sparsest swarms vary from blue to 

 greenish- white, so that the redness will gradually deepen in passing 

 from these to the mean swarms. Again, in passing from the mean 

 swarms to the most condensed ones, the redness must gradually dis- 

 appear, for we know that the stars of Group III are yellow or white. 



The following represents the colour-condition of stars of Group II 

 both more and less condensed than the mean swarms. 



