IV. Experiments to determine the difference in the length of the seconds pendulum in London and in Paris

The length of the pendulum vibrating seconds having been measured in London by the method and apparatus of Kater, and in Paris by those of Borda and Biot, and the standards of linear measure of the two countries having been referred respectively to those measurements for future verification, an endeavour was made by M. Arago in 1817 and 1818, at the instance of the Bureau des Longitudes, to bring the lengths so measured into direct comparison with each other, by ascertaining, by means of invariable pendulums conveyed intermediately between Paris and London, the difference of length that actually exists between the pendulums at those places; which difference ought also to be that between the absolute measurements. From a summary account of the proceedings on that occasion, published at the close of the 3rd volume of the Base du Systême Métrique, we learn that from certain accidental causes therein noticed, the rates of the pendulums employed were not obtained with sufficient precision to make the result conclusive.