THE ABSORPTION OF LIGHT IN OPEN STAR CLUSTERS. —Dr. P. ten Bruggencate, in the Zeitschrift fur Physik, October 31, describes an investigation of the colour indices of stars of the open clusters N.G.C. 1647, °f Prassepe and of the Hyades, and deduces that these clusters consist almost entirely of dwarf stars, as is to be expected on the assumption that they have developed from globular clusters and are of great age. Colour-brightness diagrams were prepared, in which the catalogued stars were plotted, and, with certain assumptions as to the value of the parallax, graphs corresponding to the stars of the general stellar system, as determined at the Mount Wilson Observatory, and described by Seares, were drawn on the same diagrams. It was found that in neither case did the stars of the cluster agree with the graph. This was also true of the colour-brightness diagram of the Pleiades, which has already been described by the author.