Whatever the dispersion used, the same qualification must be made in discussing the results; probably the dispersion would have to be greatly increased before the measured effective line depth becomes much greater for narrow line stars. Relative effective line depth, derived from numerous spectra made with the same dispersion, is still, however, of considerable significance. It permits us to recognize differences of surface gravity, and to form an idea of relative chromospheric depths for different classes of stars. SUMMARY 1. The investigation deals with the determination of the depth and contour of prominent absorption lines in the spectra of stars of various classes. 2. The spectra used were made with the 16-inch refractor of the Harvard Observatory, using two prisms and a special set of apertures. 3. Results are presented for eleven stars, of spectral class ranging from B0 to K0. 4. The spectra were analyzed under uniform conditions by means of the Moll thermoelectric microphotometer. The resolving power of this instrument is such that no integrating effect need be considered in discussing the results. 5. The microphotometer tracings were measured with reference to fiducial lines representing “darkness” and “clear film,” and to a line, representing the continuous background, drawn across the absorption lines. 6. The intensity drop from continuous background to line was deduced graphically from the measures. 7. The accuracy of the results is discussed in detail. a. The reliability of the plates, as judged from qualitative reproduction of detail, and from the consistency of the numerical results, is satisfactory. Effects of stray light are of negligible magnitude, and in this respect slit spectra appear to have no advantage over objective prism spectra. b. Effects of poor focus are measurable, but small. Spectra that are in such poor focus as to cause appreciable inaccuracy would be rejected from visual inspection. c. The accuracy of the microphotometer tracings is in general satisfactory. Tracings showing abnormal deflections from “darkness” to “clear film” are not susceptible of correction, and are omitted in deriving results. d. The measures upon the tracings are also of satisfactory accuracy. 8. The differences in intensity between the continuous background and various points along the line contour are tabulated for the eleven stars under discussion. 9. The general results for the intensities at the centers of lines show an interesting relation to absolute brightness; the brighter stars have, in general, lines that cut more deeply into the background. A result of considerable interest is that the average residual intensity in the strong wide absorption lines is more than 30 per cent of the background intensity. VOLUME 60. 1. DALY, REGINALD A.—The Geology of Ascension Island. pp. 1–80. 21 pls. June, 1925. $3.00.