oS 
uly 8, 1886] 
NATURE 
227 
THE SUN AND STARS! 
VIII. 
} 
FOR the purpose of this lecture I have ventured to make a 
j revision of the classification which has been suggested by Dr. 
Vogel. I should tell you, with reference to this question of 
"classification, that Rutherford started it; then the German 
physicist, Prof. Zollner, recommended a certain line of arrange- 
ment which practically had been adopted by Father Secchi. I 
afterwards saw grounds for saying that that line of arrangement, 
or sequence, was apparently a very just one, because it seemed, 
from some considerations I brought forward, that it really 
arranges the stars in the order in which the various phenomena 
_ would be produced in the atmosphere of any one of them ; that 
is to say, that it was a true evolutionary line starting from the 
conditions of highest temperature. Others have followed in the 
same track since, including Dr. Vogel; but, so far as I can 
_ make out, any credit which is due to the existing arrangement 
is due to Father Secchi and to Prof. Zollner. 
__ I will give you the arrangement, which I think will perhaps 
bring the facts in the most clear way before you. 
__ We have, then, the first class of stars with broad absorption- 
| lines and very few of them, and a remarkable absence of general 
i 5 
_ absorption at the blue end of the spectrum. Next we have a 
second class, in which the lines are more numerous, and they 
are thinner. In this class come our sun, Arcturus, Aldebaran, 
and Capella. 
_ Then we pass from absorption-lines altogether, and in the 
third class we have stars with flutings, of which the darkest part 
the spectrum, Of these stars we have a Herculis and a Orionis 
as examples. 
Then we have another set of fluted stars in which the opposite 
holds good. The darkest part and sharpest edge of the fluting 
are to the right, towards the red end of each fluting. And the 
stars of this class are faint. 
In those four classes we nearly exhaust all those forty or fifty 
millions of stars in the heavens which shine, and which we can 
study by means of a telescope. 
Afterwards we come to stars with bright lines, or the fifth class ; 
and this we must divide into two—A and B. 
In sub-class A the bright lines are always lines of hydrogen, 
such as we have in the chromosphere of the sun. Many of 
the=e stars, as we shall see by and by, which are characterised 
by such a spectrum as this are variable stars ; not all. 
In sub-class B the lines are not lines of hydrogen, and I 
may say that up to the present moment the origin of these lines 
is not known. There are, I think, at the present moment 
about half a dozen stars known with spectra of this character. 
So much, then, for a general view. We have four classes of 
stars determined by absorption—two, line absorption ; two, fluting 
absorption ; first, broad lines ; second, thin lines; first, flutings 
with the sharp dark edge to the left; then, flutings with the 
sharp dark edge to the right. Then in the last class we leave 
absorption-lines altogether and get to bright lines, and we get 
two sub-classes—those which obviously contain incandescent 
hydrogen, and those which as obviously contain something else. 
Just a word or two on each of these two classes. 
The stars with dark thick lines can be best shown by this 
and sharpest edge of the fluting lie towards the violet part of | diagram, which I owe to the kindness of Dr. Huggins. You 
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Fic. 22.—Stellar spectra (Huggins). In this diagram the spectrum of the sun is given at the top so that the spectra of the stars can be compared with it. 
The spectra of the stars are reduced from photographs, and the order of arrangement has been determined by the gradual thinning of the chief lines. 
will see the difference between the thick absorption-lines and the 
thin ones, and you will remember that although stars may have 
the absorption-lines of identical wave-lengths, the thickness of 
{ these lines in the different stars may vary from one star to the 
other. Then we have the solar spectrum, the thickest lines of 
which are H and K, already refer.ed to, in the ultra-violet 
‘portion. 
_ The remarkable thing about the stars of the first class is that 
_ msome of them H is seen alone. In others H is seen with K 
thin, and in others H is seen with K almost as thick as itself. 
| These lines are supposed to be due to the absorption of calcium. 
When calcium was studied in the laboratory a good many years 
ago, it was found that, at the temperature of the electric arc, the 
' important brilliant line of calcium—the line which outshone all 
the others—was in the blue part of the sprectrum, and that the 
_ two lines which are most important, the two broadest lines, in the 
‘Solar spectrum, are hardly seen at all in the spectrum unless 
the temperature of a very powerful induction coil be employed. 
_ Under these circumstances one may get the same relative import- 
“ance given to the lines H and K in the violet which one gets with 
| tegard to the line in the blue as seen ordinarily, but only when 
_ _* A Course of Lectures to Working Men delivered by J. Norman Lockyer, 
F.R.S., at the Museum of Practical Geology. Revised from shorthand 
| Motes. Continued from p. 207. 
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| the most tremendous means available to us are taken to secure 
what we consider to be the highest temperature. 
On that ground it was prophesied that if the spectra of stars 
were ever photographed, probably some might be found hot 
enough to deal with those bright lines, H and K, in exactly the 
same way that the electric spark did ; that is to say, that asin our 
laboratories we can get at a high temperature H and K obviously 
more brilliant than the blue line, whereas at low temperatures H 
and K are not seen at all, so we may anticipate similar results in 
the stars ; if we can get stars very much hotter than any electric 
spark which we can obtain here, we might get H and K in dif- 
ferent proportions, or each seen alone. 
Now you see that prophecy, has been fulfilled in this respect— 
that there are stars in which we get H alone without K, and we 
get different proportions of K added, as you can get different 
proportions of milk and sugar in a cup of tea. p 
Nor is that all. I am bound to tell you one other very curious 
fact. Since it was obvious when these stars were photographed 
that we were really photographing the result of an increased 
temperature ; another prophecy was hazarded, and that was, 
that when, during an eclipse, the very brightest portion of the 
sun’s atmosphere should be photographed in the ultra-violet and 
violet the spectrum would probably be very closely represented 
by the spectrum of these hottest stars. These photographs by 
