1156 
musterung’'), Einleitung S. XXIII. For our purpose they were given 
the following form: 
H. 44 — H. 14 = — 0.01 + a(e- 4.0) 
in which c is the colour-number according to Ostsorr and a a 
function of the magnitude, varying linearly. with the difference 
between the apparent brightness of the star in the two photometers, 
calculated in the manner as has been indicated on p. XXIV of the 
same introduction (for magnitude 1.0, 2.0, 3.0 we havea = + 0.062, 
+ 0.054, + 0.042). Subsequently to these magnitudes, reduced to 
H.14 and to the magnitudes of H.14 itself, the correction for 
colour was added, which has been found in my dissertation p. 158. 
There is also to be found the correction varying with the magni- 
tude which has to be added to the results with Photometer C II, 
in order to reduce them to the same system’). All stars used by 
me have been observed in Potsdam also with Photometer C III. As 
they have no excessive apparent brightness in this instrument and 
hence no variation with the brightness is to be expected in this case, 
a constant correction —0™.23 was added to the results with C III. 
For the employed comparison-stars, supplemented with a few other 
stars, continuing the scale further to the fainter side, we give suc- 
cessively : the colour according to OstHorr, (derived in the manner 
as indicated in my dissertation p. 168), next the magnitudes of Har- 
vard 14, Harvard 44, Potsdam C II and C III, all corrected in 
the way already mentioned, subsequently the adopted simple mean 
value from these four and then the brightness in the employed scale 
of comparison-stars. 
1) Publicationen Potsdam 17. 
2) Miter and Kempr have not corrected the results obtained with Cl, because 
they could not discover a systematic difference between CI and CIL (Einleitung 
S. XIV). Since, however, for the comparison of these instruments they could only 
avail themselves of stars between magnitudes 3.5 and 5.5, this does not clash 
with my result that a correction is needed for the brighter stars up to the 2ud 
magnitude, which of course can only be found by comparison with another cata- 
logue. While the comparisons employed by Mürrer and Kempr can teach nothing 
about the absence of systematic errors for these bright stars, the fact that increas- 
ing negative corrections are needed for Cl above magnitude 4.8, and for photo- 
meter D above magnitude 61 (Einleitung S. XID, renders it exceedingly probable 
that similar corrections are needed for C Il above magnitude 3.4, such as I deri- 
ved in my dissertation. The final values of the Potsdam “General Catalog” are there- 
fore likely to be systematically erroneous above the 3'¢ magnitude. For this reason 
| have not been able to use simply the Potsdam system for the magnitudes of 
the comparison-stars, as would have been a matter of course for fainter stars, 
By using the Potsdam system | should have found the amplitude too small, 
