To these figures a few remarks founded on recent observations might be made. The average distance between us and the stars in each group is different and the yellow stars, to which indeed our Sun belongs, are those nearest to us in space. They are therefore easier to observe than stars in the other groups. Campbell’s statistics include also for this reason a smaller number of stars in this class than in the others. It is conceivable and by the astronomer Halm held to be true that the mean velocity of the smaller stars is greater than that of the larger ones. This is the condition existing in a mixture of different gas molecules, with which the brilliant French scientist, Henri Poincaré, compared the throng of stars, inasmuch as the heavier molecules possess the slower motion. To confirm this W. S. Adams of the Carnegie Observatory on Mount Wilson compared stars of equal velocity in their own orbits. Such stars are considered to be on the average equally far removed from us. He found the theory of Halm confirmed. The mean velocity of the hydrogen stars was reduced from 11 km. (6.8 miles) to 7.5 km. (4.7 miles), that of the yellow stars from 15 km. (9.3 miles) to 9.2 km. (5.8 miles), and that of the red stars from 17 km. (11.5 miles) to 14 km. (8.7 miles), while that of the helium stars remained unchanged. The sequence of the stars arranged according to velocity in the line of sight is evidently not modified by this new calculation. In regard to the motion of the planetary nebulæ it should be mentioned that Campbell in this connection has carried out a great number of new determinations according to which the mean observed velocity of these large bodies in the line of sight must be increased to not less than 42 km. (26 miles) per second. Campbell and Moore contribute the following interesting data in regard to Nebula N. G. C. 7009 (Fig. 2):