SPECTRA OF SOME OF THE BRIGHTER STARS. 
721 
Continuous absorption in tbe violet begins at this stage, as will be seen on reference 
to the spectrum of Arcturus. The question of carbon absorption at this stage has 
already been referred to (p. 700). There is undoubted evidence of its presence in the 
solar spectrum, and in the spectrum of Arcturus—the only star which has yet been 
investigated with special reference to this point. 
Hence, it seems probable, as I stated in a former paper,* that “ the indications of 
carbon will go on increasing in intensity slowly, until a stage is reached, when, owing 
to the reduction of temperature of the most effective absorbing layer, the chief 
absorption will be that of carbon.” 
It is evident that all such stars will be dim, and hence their spectra have not 
been met with in this preliminary survey of the photographic spectra of the brighter 
stars. 
The phenomena we should expect on the hypothesis, in stars of decreasing tempera¬ 
ture, therefore actually appear in the series of spectra represented in Plate 29. 
The general result of the above discussion then, as far as it goes, is as follows :— 
Among the 171 stars already considered there are really two series of spectra, one 
representing the changes accompanying the increase of temperature, while the other 
represents the effects of decreasing temperature. The fundamental requirement of 
the meteoritic hypothesis is, therefore, fully justified by the discussion of the 
photographs. 
A very important point in connection with the two series of successive spectra is 
that one spectrum, such as that of a Andromedae, possesses characteristics common 
to both, and we might, therefore, connect the two series together by this spectrum. 
In that case we should find, if we commence with the first spectrum in Series 1, say 
that of a Herculis, that the continuous absorption diminishes and that the breadth of 
the hydrogen lines regularly increases, until such a spectrum as that of a Andromedae is 
reached (Plates 26 and 27). Then the condition would be reversed, the breadth of the 
hydrogen lines diminishing and the continuous absorption in the ultra-violet increasing 
in extent until such a star as Arcturus is reached (Plate 29). 
I have previously discussed the question of what spectrum is associated with the 
hottest stars,! and, generally speaking, it appears to be that in which the continuous 
‘ radiation at the violet end of the spectrum is greatest, and the hydrogen absorption 
lines are broadest.| 
' * ‘ Roy. Soc. Proc.,’ vol. 13, p. 155. 
t Bakerian Lecture, ‘Roy. Soc. Proc.,’ vol. 41, p. 26. 
t An erroneous idea witb. regard to the indications of the temperature of the stars has been held by 
I those who have not considered the matter specially. It has been imagined that the presence of the 
i series of hydrogen lines in the ultra-violet was of itself sufficient evidence of a very high temperature. 
The experiments of Cornxj^ however, have shown that the complete series of lines can be seen with an 
ordinary spark without jar. Hence, the high temperature of such a star as Sirius is not indicated by 
the fact that its spectrum shows the whole series of hydrogen lines, but by the fact that there is bright 
continuous radiation far in the ultra-violet. 
1 ‘ .lournal de Physique,’ vol. 10, 1886. 
4 Z 
I 
MDCCCXCIII.—A. 
