The Colors of 1332 B Stars.

The colors of 1332 stars of spectral types B, 0, cB, and cA have been measured with a photoelectric cell at Madison or at Mount Wilson. The list includes neirly all 0-B5 stars north of - ~ declination and brighter than visual magnitude 7.~, and, in addition, nearly all O-B2 stars north of __4Q0 of whatever magnitude to the limit of the Henry Draper Catalogue. The effective wave lengths of the cell with the two friters used and for an equal- energy source are 4260 and 4770 A. The scale of the colors is close to two-thirds of the international scale. The probable error of a color index is ± 0.02 to ± 0.03 mag. for Madison, and ± 0.01 to ± 0.02 mag. for Mount Wilson. The color excesses of B stars are correlated with the intensities of interstellar lines. The space reddening is greater toward the center than toward the anticenter of the galaxy. Even the brightest regions of the Milky Way are partially obscured. The ab- sorption in the galaxy is not uniform but spotted and irregular