DR, W. HUGGINS ON THE PHOTOGRAPHIC SPECTRA OF STARS. 
685 
Lines. 
H 4340 
/I 3834 
h 4101 
7 3795 
H 2 3968 
O 3767-5 
K 3933 a strong line, nearly as 
3757 - 5 
strong as H r 
e 3745-5 
* 3887-5 
£ 3730 
3862-5 
n 3717-5 
§ XV. Arcturus. 
In this spectrum we have to do with a different order of suns, and have now 
entered upon the solar class of stars. The line K is very broad and winged, more so 
than H and is stronger than it is in the solar spectrum. 
In the eye observations by Dr. Miller and myself we said: “ This is a red star, 
the spectrum of which somewhat resembles that of the sun. In this we have 
measured upwards of thirty lines and ascertained the existence of a double sodium line 
at D.”* The triple line of magnesium coincident with b is so well seen in the 
spectrum of this star that I made use of these lines in my determination of the star’s 
motion in the line of sight in 1871. 
In the photographic spectrum a great many lines are seen in the part of the 
spectrum which is less refrangible than that included in my map, namely, from about 
b to G. The whole photographic spectrum is crowded with lines similar in general 
characters to those of the solar spectrum. Twenty-one of the stronger of these lines 
have been measured and are given in the map. Several of these agree in position 
with similar lines in the solar spectrum. 
On the more refrangible side of h the appearance of a bright band is seen which 
suggests a bright line. After a careful examination of the two negatives which I have 
of this star, and of positives taken from them, I have come to the conclusion that 
this appearance is really due to the absence of the finer lines which probably crowd 
the other parts of the spectrum, though they are too fine and close to be seen 
separately in the photographs. 
Beyond K we have a strong contrast presented in the character of the lines. Here 
the lines are much broader and more intense, and arranged more or less in triple and 
other forms of grouping with finer lines between. 
The stronger lines only of the crowded spectrum have been measured and inserted 
m the map. There are lines corresponding to some of the lines of the Vega class. 
The dissimilarity of this spectrum from the class of white stars is further seen in 
the circumstance that as far as the spectrum can be traced upon the plate it is crowded 
mdccclxxx. 
* Phil. Trans. 1864, p. 428. 
4 T 
