The clustering of the nebulae here recorded is very pronounced. In the center of Field III there are some 75 nebulae scattered over an area equal to that subtended by the full moon.[7] In order to examine the distribution of the different sizes, diameters were plotted against frequencies. The small scale of the plates renders the number of smallest diameters very uncertain. Nebulae less than 10″ in diameter might easily be mistaken for stars and overlooked, especially if they are at some distance from the center of the field. The curves resemble probability-curves, as one would expect for random distribution in a cluster at a definite distance. [7] See Plate IV, enlarged from negative R 3352, taken with 120ᵐ exposure on February 26, 1916. The numbers were marked on only those nebulae which promised to be readily visible on the engraving, and which were separated enough to give room for inscribing the number. The B.D. stars are designated by letters, for which the key is as follows. FIELD III STAR B.D. A = +30°2107 B = +30°2108 C = +30°2109 D = +30°2110 E = +30°2115 F = +30°2121 G = +30°2123 H = +29°2123 J = +29°2125 K = +29°2126 L = +29°2128 M = +29°2129 N = +29°2130 P = +29°2133 R = +29°1970 S = +28°1971 TABLE IV DISTRIBUTION ACCORDING TO SIZE OF THE NEBULAE IN THREE FIELDS =========+===================+============== | FIELD | DIAMETER +-------------------+ WOLF’S FIELD | I | III | VII | IN PERSEUS ---------+-----+------+------+-------------- 5″ | | | | 3 10 | 7 | 38 | 5 | 34 15 | 27 | 67 | 12 | 52 20 | 25 | 42 | 18 | 26 25 | 6 | 19 | 10 | 6 30 | 5 | 9 | 4 | 2 35 | 3 | 2 | 4 | 1 40 | 4 | 5 | 4 | 2 45 | 1 | 3 | 3 | 50 | 1 | | 3 | 60 | | | 3 | 90 | | | 1 | ---------+-----+------+------+--------------