2. The work on the Harvard spectrograms has been carried out by the method that was described in the preliminary report (H.B. 805, 1924). The plates were all made with the sixteen-inch refractor, using two prisms and a special set of apertures. The different apertures provide relative objective areas of 16, 8, 4, 2, and 1, respectively. The apertures are rectangular, and the successive reducing strips are placed perpendicular to the refracting edge of the prism. It is assumed in the discussion that the amounts of light admitted by the apertures are in the same ratio as their areas. A standard procedure has been adopted in securing the spectrograms. A series of spectra with the several apertures was obtained upon each plate. Focus, clock rate, and exposure time were kept constant over any one series. In general the apertures were used in the order 16, 8, 4, 2, 16. Aperture 1 was omitted in nearly every case, and for a few stars other apertures were also omitted, or found to be useless owing to faintness of the image. Omission of apertures is indicated by notes to Table I. TABLE I LIST OF PLATES USED ┌────────┬───────────────┬────────┬─────────────────┬─────────────────┐ │ Plate │ Star │Spectral│ Apertures │ Remarks │ │ Number │ │ Class │ │ │ ├────────┼───────────────┼────────┼─────────────────┼─────────────────┤ │MC 20790│α Lyrae │ A0│1, 16a, 8, 4, 2 │Ap. 2 not used │ │ 20797│α Bootis │ K0│1, 16a, 8, 4, 2, │Ap. 1 and 2 not │ │ │ │ │ 16b │ used │ │ 20800│α Aquilae │ A5│1, 16a, 8, 4, 2, │Ap. 1 and 2 not │ │ │ │ │ 16b │ used │ │ 21640│α Cygni │ cA2│16a, 8, 4, 2, 16b│ │ │ 21645│δ Cassiopeiae │ A5│16a, 8, 4, 2, 16b│ │ │ 21646│α Cassiopeiae │ K0│16a, 4, 2, 16b │Ap. 16b not used │ │ 21721│α Aurigae │ G0│16a, 8, 4, 2, 16b│ │ │ 21722│δ Canis Majoris│ cF8│16a, 8, 4, 2, 16b│Ap. 16b not used │ │ 21788│β Orionis │ cB8│16a, 8, 4, 2, 16b│Ap. 16b not used │ │ 21789│ε Orionis │ B0│16a, 8, 4, 2, 16b│Ap. 16b not used │ │ 21802│α Canis Majoris│ A0│8, 16, 4, 2 │ │ └────────┴───────────────┴────────┴─────────────────┴─────────────────┘ The apertured spectra were examined, and any that showed irregularities were rejected. In cases of interference by clouds, whether or not the spectra were visibly impaired, the plates were not measured. Spectra which appeared from experience to be too strong or too weak for satisfactory analysis were also rejected.