The _Proceedings_, begun in 1878, are intended for the publication, in separate form, of shorter papers from the Museum of Natural History. These are gathered in volumes, octavo in size, with the publication date of each paper recorded in the table of contents of the volume. In the _Bulletin_ series, the first of which was issued in 1875, appear longer, separate publications consisting of monographs (occasionally in several parts) and volumes in which are collected works on related subjects. _Bulletins_ are either octavo or quarto in size, depending on the needs of the presentation. Since 1902 papers relating to the botanical collections of the Museum of Natural History have been published in the _Bulletin_ series under the heading _Contributions from the United States National Herbarium_, and since 1959, in _Bulletins_ titled "Contributions from the Museum of History and Technology," have been gathered shorter papers relating to the collections and research of that Museum. The present collection of Contributions, Papers 34-44, comprises Bulletin 240. Each of these papers has been previously published in separate form. The year of publication is shown on the last page of each paper. FRANK A. TAYLOR _Director, United States National Museum_ * * * * * Contributions from the Museum of History and Technology: Paper 44 DEVELOPMENT OF GRAVITY PENDULUMS IN THE 19TH CENTURY by Victor F. Lenzen and Robert P. Multhauf GALILEO, HUYGENS, AND NEWTON 304 FIGURE OF THE EARTH 306 EARLY TYPES OF PENDULUMS 309 KATER'S CONVERTIBLE AND INVARIABLE PENDULUMS 314 REPSOLD-BESSEL REVERSIBLE PENDULUM 320 PEIRCE AND DEFFORGES INVARIABLE, REVERSIBLE PENDULUMS 327 VON STERNECK AND MENDENHALL PENDULUMS 331 ABSOLUTE VALUE OF GRAVITY AT POTSDAM 338 APPLICATION OF GRAVITY SURVEYS 342 SUMMARY 346 VICTOR F. LENZEN AND ROBERT P. MULTHAUF DEVELOPMENT OF GRAVITY PENDULUMS IN THE 19th CENTURY