ARTICLE III. DISCUSSION OF THE MAGNETIC AND METEOROLOGICAL OBSERVATIONS MADE AT THE GIRARD COLLEGE OBSERVATORY, PHILADELPHIA, IN 1840, 1841, 1842, 1843, 1844, AND 1845. Fourth Section, comprising Parts X, XI, AND XII. DIP AND TOTAL FORCE. ANALYSIS OF THE DISTURBANCES OF THE DIP AND TOTAL FORCE; DISCUSSION OF THE SOLAR DIURNAL VARIATION AND ANNUAL INEQUALITY OF THE DIP AND TOTAL FORCE; AND DISCUSSION OF THE ABSOLUTE DIP, WITH THE FINAL VALUES FOR DECLINATION, DIP AND FORCE BETWEEN 1841 AND 1845. By A. D. BACHE, LL. D., F. R. S., Mem. Corr. Acad. Sc. Paris; Prest. Nat. Acad. Sciences; Superintendent U. S. Coast Survey. Pp. 44. (Published January, 1865.) ARTICLE IV. ON THE CONSTRUCTION OF A SILVERED GLASS TELESCOPE, FIFTEEN AND A HALF INCHES IN APERTURE, AND ITS USE IN CELESTIAL PHOTOGRAPHY. By HENRY DRAPER, M. D., Professor of Natural Science in the University of New York. Pp. 60. (Published July, 1864.) §1. Grinding and Polishing the Mirrors 2 §2. The Telescope Mounting 27 §3. The Clock Movement 38 §4. The Observatory 41 §5. The Photographic Laboratory 46 §6. The Photographic Enlarger 51 ARTICLE V. PALÆONTOLOGY OF THE UPPER MISSOURI: A REPORT UPON COLLECTIONS MADE PRINCIPALLY BY THE EXPEDITIONS UNDER COMMAND OF LIEUT. G. K. WARREN, U. S. Top. Engrs., IN 1855 AND 1856. INVERTEBRATES. By F. B. MEEK AND F. V. HAYDEN, M. D. Part I. Pp. 158, and five Plates. (Published April, 1865.) Introductory Remarks vii I. Silurian Age. Potsdam Period 1 II. Carboniferous Age. Carboniferous Period 11 III. Carboniferous Age. Permian Period 48 IV. Reptilian Age. Jurassic Period 66 Index 121 Explanations of Plates. ARTICLE VI. CRETACEOUS REPTILES OF THE UNITED STATES. By JOSEPH LEIDY, M. D., Professor of Anatomy in the University of Pennsylvania, Curator of the Academy of Natural Sciences of Philadelphia. Pp. 140 and twenty plates. (Published May, 1865.)