8 
RESEARCHES IN STELRAR PHOTOMETRY. 
The methods available for determining the wedge absorption can be classed 
under two heads: (i) Measurements of standard stars whose magnitudes have 
been well fixed; (2) measurements of an artificial star whose light can be reduced 
by a known amount either by (a) polarization, ( b ) a revolving wheel, (c) reduced 
apertures by stationary diaphragms. The last method can be used either with 
real or artificial stars. The method by standard stars seems to give the best 
results, as it has the great advantage that the measurements are made under 
the same conditions as exist in practice. 
magnitude 
0 _ t _2_J_4_ i > 
Hi 
Fig. 3. —Curve E 6. Absorption of Wedge V on 6-inch Reflector. 
The errors which may be introduced by the neglect of this precaution are dealt 
with by King in Harvard Annals, 41 , pages 237 et seq., where it was found that 
the mean absorption corresponding to one scale division was 0.090 with the wedge 
almost in contact with the aperture, and 0.130 with the wedge 5 cm. from the aper¬ 
ture. Again, it was found by Aitken and Maddrill (Astrophysiccil Journal, 22 , 147) 
that the absorption measured with a Tummer-Brodhun photometer, comparing 
surfaces, must be increased by one-quarter to equal the results obtained from stand- 
