{Science Press; Science Progress; Scientia; Scientific American; Scientific International Research Service Corp.; E. M. Scofield; Charles Scribner's Sons; N. P. Scudder; H. von Seeliger; Seismological Society of America; Selznick International Pictures, Inc. [W. E. McCune]; Service; Geneva Seybold; James A. Shanahan; W. N. Shaw; Barbara Sheffield}
{Ibérica; Indian Academy of Sciences [M. N. Saha]; Institut d'Astronomique Pratique, Warsaw, Poland; Institut d'Optique; Institut de Physique du Globe, Paris [Ch. Maurain]; Institute of International Education; International Catalogue of Scientific Literature; International Education Board [re grant for AAVSO]; International Magazine Co.; International Press Service; Irving-Pitt Manufacturing Co.; Dorothea Isaac-Roberts}
{Salto Observatory; Sanborn, Vail & Co.; San Diego Business and Professional Women's Club; San Diego County Planning Commission; San Diego Scientific Library; E. Sanger-Sheppherd; W. W. Sargeant; A. P. Saunders; Frederick A. Saunders; George G. Saunders}
{Felix M. Perez [Sanchez]; T. P. Perkins; Nicolas Perrakis; C. D. Perrine; Max Petersen; John E. Pfeiffer; Philadelphia Inquirer [John Miller]; "Pinacyanol" [advert from Lucius & Brüning Farbwerke]; Harry Hemley Plaskett; Poggendorff's Biographisch-Literarisches Handwörterbuch; Popular Astronomy; Popular Science Monthly [Sumner Blossom]; M. A. Porcabeuf; J. G. Porter; Potsdam Astrophysical Observatory [H. von Klüber; E. F. Trondlich]; Poulkovo Observatory; N. R. Powley; Poznan Observatory [Joseph Witkowski]; Irwin G. Priest; Henry S. [& Mrs.] Pritchett; S. Procopin; W. S. Prosser; Herbert Putnam; G. P. Putnam's Sons; W. F. Quarrie & Co. [S. E. Farquhar]}
{Sigma Xi; L. Silberstein; Edward E. Simonds; Frederick Simpich; Arthur W. Sinclair; A. de Sitter; W. T. Skilling; Sarah Louise Slaughenhaup; Paul Slavenas; Frederick Slocum; E. E. Slosson}
{Leo J. Scanlon; William C. Scarritt; Robert O. Schad; Paul W. Schenck; James A. B. Scherer; Frank H. Schleer; Carl Schleicher & Schüll; Hans W. Schneider; Dorothy E. Schoof; J. Schroeter; F. Schuerer; L. Schützenberger; A. Schwassmann}
{Albert Chase McArthur; Macbeth Daylighting Co., Inc. [Norman Macbeth]; Lucena McBride; Phoebe Merl McClees [ltrs M. E. Churchill ?? FHS; FHS ? Fisk Teachers' Agencies]; Frank McCoy; E. C. MacDowell; Anita Newcomb McGee; McGill University; Dean B. McLaughlin; MacMillan Co. Publishers [Rose Levy]; Mrs. John McMillan; Maud W. Makemson; E. Mallinckrodt, Jr.; Marburg University Library; Marchaut Calculating Machine Co. [folded]; W. L. Marcy; Marina, Instituto y Observatorio de; Marquis, A. N. & Co.}
