ASTRONOMY: W. S. ADAMS 
151 
absolute magnitudes the ordinates. The stars were divided into five 
groups according to spectral type and curves were drawn for each group. 
The groups are as follows: 
F0-F6; F7-G7; G8-K4; K5-K9- M 
The curves are so nearly straight lines in the case of the first three of 
these groups that straight lines have been adopted, the constants being 
derived by least square solutions. In the K5-K9 group the curve for 
(a) is a straight line but not for (b) or (c) . It is probable that there are 
no straight lines in the M group, but this is very uncertain. The sig- 
nificance of a straight line is, of course, that the intensity of the spectrum 
line varies uniformly with the absolute magnitude. 
The most serious difficulty in the construction of these curves is the 
scarcity of parallax determinations on stars of high luminosity. Paral- 
lax observers have confined their attention almost wholly to stars of 
large proper motion which promise to yield large parallaxes. With the 
aid, however, of the Yale observations on the very bright stars, and some 
most valuable determinations by Mr. van Maanen of the parallaxes of 
certain stars of small proper motion, a number of stars of very high 
luminosity were selected upon which the lower portions of the curves 
could be based. Particularly in the cases of the K5-K9 and the M 
groups these portions of the curves are still most uncertain, and must 
be adjusted with the aid of additional parallax observations when they 
become available. 
The list of formulae derived for the several groups is given in Table I. 
The equations are from my own observations. A similar list, in which 
the constants differ slightly, has been obtained from the determinations 
of Miss Burwell, who has carried out a complete series of estimations of 
the line intensities in these stars. In the formulae, M is the absolute 
magnitude, and A the estimated difference of intensity for each of the 
pairs of lines. 
TABLE I 
(a) 
(b) 
(c) 
F(>-F6 
M = 
-1.9A +5.2 
M = 
+2. OA +3.3 
M = 
+2.8A - 
-2.6 
F7-G7 
M = 
-1.4A +4.9 
M = 
+2. OA +3.3 
M = 
+2.8 A - 
-2.6 
G8-K4 
M = 
-1.6A +4.7 
M = 
+ 1.6A +5.1 
M = 
+2.3 A - 
-0.3 
K5-K9 
M = 
-1.8 A +5.0 
Curve 
Curve 
M (low luminosity).. 
.M = 
-1.5 A +6.9 
Curve 
Curve 
The equation and curves in the case of the M stars are applicable 
only to the stars of low luminosity. In the case of the F0-F6 stars it 
is doubtful whether the equations given, which for (b) and (c) are the 
same as in the G group, are other than rough approximations. The en- 
