d. _Accuracy of measures._ In comparison with the errors of the plates and of the microphotometer tracings, the errors in the measurement of the records are of relative unimportance. The chief difficulty, as mentioned above, is that of drawing from fiducial points the reference lines representing the continuous background and the “clear film.” The error thus introduced may occasionally amount to one millimeter, or two divisions of the scale. It is sometimes difficult to decide upon the position of the center of a line, especially when it is wide, without a sharp maximum. This may lead to large residuals for measures on the wings, especially for such lines as Hε and Hζ. 8. The results of the investigation are given in Table IX, which contains, in successive columns, the name of the line, the wave length, expressed to the nearest Angstrom, the mean value of the difference of intensity, background _minus_ line, expressed in stellar magnitudes, the residuals, the “selected mean” value of the same intensity difference (see Section 6) and its residuals. The stars are mentioned at the beginnings of their respective records, and are arranged in order of plate number. In the case of stars for which no “selected mean” is quoted, all the values used for the mean conform to the criterion for “selected mean.” TABLE IX DIFFERENCES OF INTENSITY, BACKGROUND _minus_ LINE ┌───────────┬──────┬──────────┬────────────────────┬──────────┬───────────────┐ │ Plate and │ Wave │ Mean │ Residuals │ Selected │ Residuals │ │ Star │Length│Intensity │ │ Mean │ │ │ │ │Difference│ │Difference│ │ ├───────────┼──────┼──────────┼────────────────────┼──────────┼───────────────┤ │MC 20790 │4877 │ .11│1, _4_, 4 │ .11│_4_, 4 │ │α Lyrae │4872 │ .23│2, _3_, 2 │ .23│_3_, 2 │ │ │4866 │ .49│_2_, 1, 1 │ .50│ │ │ │4861 │ .95│_10_, 0, 7, 5 │ .95│ │ │ │Hβ │ │ │ │ │ │ │4856 │ .73│2, _3_, 2, _3_ │ .73│_3_, 2 │ │ │4851 │ .35│_5_, 5, 2, _3_ │ .38│2, _1_ │ │ │4846 │ .17│_5_, 3, 3, 0 │ .19│1, 1, _2_ │ │ │4840 │ .07│_2_, 0, 3, _2_ │ .07│0, 3, _2_ │ │ │4358 │ .11│_6_, _9_, 6, 6, 1 │ .10│_8_, 7 │ │ │4354 │ .23│_11_, _1_, 9, 4 │ .27│_5_, 5 │ │ │4349 │ .45│_15_, 0, 15, 2 │ .52│_7_, 8 │ │ │4345 │ .83│8, _3_, 19, _8_ │ .86│_6_, 16, _11_ │ │ │4340 │ 1.43│_6_, 19, _6_, _3_, │ 1.62│ │