152 
HAGEN. 
Osthoff (Astron. Nachr. Bd. 153, 1900). His catalogue differs 
from the former principally in denoting colors by figures, 
from 0 to 10, instead of letters. He uses, as did Krueger 
and Safarik, the historical scale of Schmidt. 
The importance of color corrections in comparing photo¬ 
metric measures was discussed by Pannekoek at the Diissel- * 
dorf meeting of the “ Vereinigung von Freunden der Astron- 
omie, etc.” (Mitteilungen X Jahrg., 1900). He starts from 
the Young-Helmholz theory of the three fundamental sen¬ 
sations, Red, Green, Blue (R, G, B), and expresses the 
brightness of stars in the PD. by the formula: 
Brightness = 0.57 R -f 0.32 G — 0.07 B. 
Another example he gives in reducing Plassmann’s scale 
of steps of the comparison stars of Algol to the PD. scale by 
the two formulas: 
(I.) Mag. = 4.08 — 0.081 Steps , without 
color correction; 
(II.) Mag. = 4.08 —0.081 Steps — 0.08 (C—3.3), with color 
correction, 
where 0.081 and 0.8 are the assumed values of one step in 
brightness and color respectively, and C denotes the color of 
the star in Osthoff’s catalogue. The first formula leaves a 
mean difference from the PD. = ±0.10 mag., the second a 
difference of only 0.04 mag. Since these will be the very 
stars needed for determining the brightness of the new star 
that appeared last week in Perseus, we give the complete 
table : 
Star. 
PD. 
Osthoff. 
Plass. 
I. 
A 
II. 
A 
M. 
C. 
St. 
M. 
M. 
v Persei. 
4.02 
3.8 
0.0 
4.08 
—0.06 
4.04 
—0.02 
a Trianguli. 
3.65 
4.1 
5.0 
3.68 
—0.03 
3.62 
+0.03 
8 Persei. 
3.33 
2.3 
10.0 
' 3.27 
+0.06 
3.35 
—0.02 
c Persei. 
3.16 
2.0 
13.2 
3.01 
+0.15 
3.11 
+0.05 
y Andromedse.... 
2.39 
5.6 
18.7 
2.57 
—0.18 
2.39 
0.00 
0 Persei. 
2.50 
1.8 
21.1 
2.37 
+0.13 
2.49 
+0.01 
a Persei. 
2.18 
3.5 
22.7 
2.24 
—0.06 
±0.10 
2.22 
—0.04 
±0.04 
