taken to avoid temperature errors. Ferdinand Rudolph Hassler's use of the metre in coastal survey, which had been an argument for the introduction of the Metric Act of 1866 allowing the use of the metre in the United States, probably also played a role in the choice of the metre as international scientific unit of length and the proposal, in 1867, by the European Arc Measurement (German: Europäische Gradmessung) to “establish a European international bureau for weights and measures”. The European Arc Measurement decided the creation of an international geodetic standard for measuring baselines at the General Conference held in Paris in 1875. The Paris Conference of the European Arc Measurement also dealt with the best instrument to be used for the determination of gravity. After an in-depth discussion in which an American scholar, Charles Sanders Peirce, took part, the association decided in favor of the reversion pendulum, which was used in Switzerland, and it was resolved to redo in Berlin, in the station where Friedrich Wilhelm Bessel made his famous measurements, the determination of gravity by means of apparatus of various kinds employed in different countries, in order to compare them and thus to have the equation of their scales. The progresses of metrology combined with those of gravimetry through improvement of Kater's pendulum led to a new era of geodesy. If precision metrology had needed the help of geodesy, it could not continue to prosper without the help of metrology. Indeed, how to express all the measurements of terrestrial arcs as a function of a single unit, and all the determinations of the force of gravity with the pendulum, if metrology had not created a common unit, adopted and respected by all civilized nations, and if in addition one had not compared, with great precision, to the same unit all the rulers for measuring geodesic bases, and all the pendulum rods that had hitherto been used or would be used in the future? Only when this series of metrological comparisons would be finished with a probable error of a thousandth of a millimetre would geodesy be able to link the works of the different nations with one another, and then proclaim the result of the measurement of the Globe. The reversible pendulum built by the Repsold brothers was used in Switzerland in 1865 by Émile Plantamour for the measurement of gravity in six stations of the Swiss geodetic