Relation Between Color Index and Effective Wave Length from the Observations of Hertzsprung and Vanderlinden.

The investigation is concerned, first, with a recalibration of the effective wave lengths corresponding to photographic magnitudes observed by Hertzsprung and by Vanderlinden in terms of revised color in- dices on the International System; second, with a comparison of the resulting functional relations be- tween C and X with the corresponding theoretical relation computed for black-body radiators in Mt. W. Conir., No. 683. The regression formulae for reducing the observations to the International System (Table 4 and eq. [12]), which are based on the statistical investigation in the preceding Contribution, No. 698, may also be used for reducing other observations by Hertzsprung (those for NGC 1647 require an additional zero- point correction) and by Vanderlinden, made under the same conditions as those of the polar stars. The agreement of the computed and the observed relations between X and C is shown by equations (1), (25), and (26). The theoretical range of 400 A in X for photographic magnitudes, for the temperature in- terval 30,0000_3,0000, is confirmed; and the zero points agree within the inherent uncertainty-the equiv- alent of about 0.1 mag. in C. The computed effective wave lengths can therefore be used for all the ordi- nary calculations for which these quantities are required