Color Excesses for Supergiants and Classical Cepheids.IV. on Systems for Determining Color Excesses.

Period-mean color relations are derived for 24 classical cepheids whose excesses were determined by Kron and Svolopoulos; 22 of these stars were also observed by Kraft. Absolute magnitudes are estimated by the method of Paper III. The Kron-Svolopoulos and Kraft excesses differ up to 0.16 mag. (B - V) for individual stars, though most cases are much smaller. However, if excesses are estimated from period- mean color relations, these differences are considerably suppressed and lead to an effect cf less than 5 per cent in the determination of cepheid distances.