Vol.. 8, 1922 
ASTRONOMY: ADAMS AND JOY 
175 
The following table gives the absolute magnitudes M of the stars 
arranged according to spectral type. 
NO. 
M 
MA7 
NO. 
M 
MA7 
NO. 
M 
MA7 
B9n 
9 
+0.83 
+2.4 
A2n 
12 
+ 1.59 
+2.4 
A4+A5 
11 
+2.10 
2.6 
AOn 
14 
1.09 
2.4 
A2s 
7 
0.51 
2.2 
A6+A7 
11 
2.24 
2.3 
Aln 
12 
0.91 
2.0 
A3n 
7 
1.59 
2.2 
A8+A9 
10 
2.58 
2.3 
Als 
4 
0.15 
2.4 
A3s 
8 
1.18 
2.3 
Fo+Fi+F, 
. 4 
2.82 
2.3 
An inspection of these results shows a steady increase in the values of 
the absolute magnitude with advancing spectral type and a marked differ- 
ence in brightness between the stars of the same type according as the lines 
are diffuse or sharp. At type A4 and later no distinction is made as re- 
gard this latter characteristic except in the case of (;-stars. 
If these results are plotted and curves drawn through them we can from 
the curves read off the average absolute magnitude for each spectral type. 
These are as follows : 
DIPPUSE 
SHARP 
DIFFUSE 
ARP 
B8 
+0.4 
A5 
+2.1 
+ 1.8 
B9 
0.7 
A6 
2.2 
2.1 
AO 
1.0 
A7 
2.3 
Al 
1.2 
0.0 
A8 
2.5 
A2 
1.5 
0.6 
A9 
2.6 
A3 
1.7 
1.2 
FO 
2.7 
A4 
1.9 
1.5 
Fl 
F2 
2.8 
2.9 
Finally if the absolute magnitudes of the original groups of stars are all 
reduced to the same spectral type A 7 by means of these curves we obtain 
the results given under MA^ in the first table. These show a remarkable 
degree of accordance, the total range among the groups being from 2.0 to 
2.6 with an average deviation from the mean of 0.1 magnitude. 
Within the groups themselves the probable error for an individual star 
is given below. This assumes that there is no dispersion in absolute 
magnitude around the mean value for a group of stars of a given spectral 
type with definite characteristics to their lines. That the observational 
results indicate this dispersion to be small is shown by the moderate size 
of the probable errors in spite of the fact that these are in some cases probably 
increased greatly by errors in the trigonometric parallaxes. 
NO. 
NO. 
A9n 
9 
±0.48 
A3n 
7 
=t0.54 
AOn 
14 
0.46 
A3s 
8 
0.07 
Aln 
12 
0.75 
A4+A5 
11 
0.49 
Als 
4 
0.16 
A6+A7 
11 
0.69 
A2n 
12 
1.02 
A8+A9 
10 
1.24 
A2s 
7 
0.67 
F0+F1+F2 
4 
0.91 
