May 18, 1899] 
NATURE 
53 
the spectral lines. Hence the various groups defined by 
the behaviour of unknown lines were referred to by 
numbers, and as the views of those employed in the 
work of classifying differed widely as to the sequence of 
the phenomena observed, the numerical sequences vary 
very considerably so that any coordination becomes 
difficult and confusing. 
Recent work has thrown such a flood of light on the 
chemistry of the stars that most definite chemical group- 
ings can now be established, and the object of the 
present communication is to suggest a general scheme 
of classification in which they are employed, in relation 
to the line of cosmical evolution which I have developed 
in former papers communicated to the Society. 
The fact that most of the important lines in the photo- 
graphic region of the stellar spectra have now been 
traced to their origins renders this step desirable, 
although many of the chemical elements still remain 
to be completely investigated from the stellar point of 
view. 
The scheme is based upon a minute inquiry into the 
varying intensities, in the different stars, of the lines and 
flutings of the under-mentioned substances :— 
Certain unknown elements (probably gaseous, unless 
their lines represent “principal series”) in the hottest 
Stars, and the new form of hydrogen discovered by 
Prof. Pickering (which I term proto-hydrogen for the 
sake of clearness). Hydrogen, helium, asterium, cal- 
cium, magnesium, oxygen, nitrogen, carbon, silicium. 
Iron, titanium, copper, manganese, nickel, chromium, 
vanadium, strontium ; the spectra being observed at the 
highest available spark temperatures. The lines thus 
observed I term enhanced lines, and I distinguished the 
kind of vapour which produces them by the affix proto, 
é.g. proto-magnesium, for the sake of clearness.! 
Iron, calcium, and manganese at arc temperatures. 
Carbon (flutings) at arc temperatures. 
Manganese and iron (flutings) at a still lower tem- 
perature. 
In a communication to the Society? I stated the results 
arrived at recently with regard to the appearances of the 
lines of the above substances in stars of different tem- 
peratures, and the definition of the different groups or 
genera to be subsequently given are based upon the map 
which accompanied the paper, together with more minute 
inquiries on certain additional points, the examination 
into which was suggested as the work went on. 
So far as the inquiry has at present gone, the various 
most salient differences to be taken advantage of for 
grouping purposes are represented in the following stars, 
the information being derived from the researches of 
Prof. Pickering* and Mr. McClean,‘ as well as from the 
Kensington series of photographs. 
Hottest Stars. 
Two stars in the constellation Argo (« Puppis and 
y Argis).° 
Alnitam (e Orionis). This is a star in the belt of Orion 
shown on maps as Alnilam. Dr. Budge has been good 
enough to make inquiries for me which show the change 
of letter to have been brought about by a transcriber’s 
error, and that the meaning of the Arabic word is “a belt 
of spheres or pearls.” 
Stars of intermediate Temperature ( Ascending Series ). 
B Crucis, € Tauri, Rigel, a Cygni, [ ] Polaris, Alde- 
baran. 
1 Roy. Soc. Proc., vol. Ixiv. p. 398. 
2 Roy. Soc. Proc., vol. \xiv. p. 396. 
3 Astro.-Phys. Journ., vol. v. p. 92, 1897. 
4 ‘Spectra of Southern Stars.” 
5 The spectrum of this star contains bright lines, but I show in a paper 
nearly ready for communication to the Society, that when these occur with 
dark lines, the latter alone have to be considered for purposes of chemical 
classification. 
NO. 1542, VOL. 60] 
Stars of intermediate Temperature ( Descending Series ). 
Achernar, Algol, Markab, [ ] Sirius, Procyon, 
Arcturus. 
Stars of lowest Temperature. 
Ascending Series. Descending Series. 
Antares, one of the brightest 19 Piscium, one of the 
stars in Duner’s observations of | brightest stars in Duner’s 
Class IIIa.! Class III. 
[Nebule. ] (Dark Stars. ] 
In order to make quite clear that both an ascending 
and a descending series must be taken into account, I 
give herewith two photographs showing the phenomena 
observed on both sides of the temperature curve in re- 
versing layers of stars of nearly equal mean temper- 
atures, as determined by the enhanced lines. The stars 
in question are :— 
Sirius (descending). 
a Cygni (ascending). f 
Procyon (descending), | 
vy Cygni (ascending). f 
The main differences to which I wish to draw attention 
are the very different intensities of the hydrogen lines in 
Sirius and a Cygni, and the difference in the width and 
intensities of the proto-metallic and metallic lines in 
Procyon and y Cygni. 
These differences, so significant from a classification 
point of view, were first indicated in a communication to 
the Society in 1887,2 and the progress of the work on 
these lines has shown how important they are. 
I have based the group—or generic—words upon the 
following considerations. 
As we now know beyond all question that a series of 
geological strata from the most ancient to the most 
recent brings us in presence of different organic forms, 
of which the most recent are the most complex, it is 
natural to suppose that the many sharp changes of 
spectra observed in a series of stars from the highest 
temperature to the lowest brings us in presence of a 
series of chemical forms which become more complex as 
the temperature is reduced. Hence we can in the stars 
study the actual facts relating to the workings of in- 
organic evolution on parallel lines to those which have 
already been made available in the case of organic 
evolution. 
If then we regard the typical stars as the equivalents 
of the typical strata, such as the Cambrian, Silurian, 
&c., it is convenient that the form of the words used to 
define them should be common to both ; hence I suggest 
an adjectival form ending in zam. 
If the typical star is the brightest in a constellation, I 
use its Arabic name as root ; if the typical star is not 
the brightest, I use the name of the constellation. 
The desideratum referred has to a certain extent 
determined the choice of stars where many were avail- 
able. I have to express my great obligations to Dr. 
Murray for help generously afforded in the consideration 
of some of the questions thus raised. The table runs as 
follows :— 
Highest Temperature, Simplest Chemistry. 
Argonian. 
Alnitamian. 
<  Crucian. Achernian 3 
‘$ Taurian. Algolian ix 
4 Rigelian. | Markabian 
s) Cygnian. 2 
S Sirian. = 
S$ Polarian. | Procyonian, & 
$  Aldebarian. Arcturian, = 5 
5 skute! S 
~~ Antarian. Piscian, Q 
The chemical definitions of the various groups or 
genera are as follows :— 
1 “ Sur les étoiles & spectres de la troisiéme classe.” 
2 Roy. Soc. Proc.. vol. xi. p. 182. 
