Correspondence and papers regarding the determination of the longitude of Paris by observing set stars and taking the difference between the local time and Greenwich Time received by telegraphic signal. The papers include a piece, in French, on the difference in the longitudes of the Paris and Greenwich Observatories, found in 'Compte Rendu des séances de l'Academie des Sciences'; an article for the daily papers on the experiment to determine Paris' longitude; a piece on the project, in French, found in 'L'Institut'; notes on the arrangement for the tests; comparisons of observations and clock times of signals taken by various observers at Paris and Greenwich; computations of the time occupied in the passage of a signal; papers on the preparation of star places; material on the formation of Greenwich sidereal time, with the difference between the Greenwich and Paris sidereal times; abstracts of sidereal times of signals, with comparisons between Paris and Greenwich; and the difference in longitude between Paris and Greenwich. The correspondents include E. Dunkin, J.C. Clark, P.A.E. Laugier, J.B. Pentland, J.W. Brett, U.J.J. Le Verrier, Y. Villarceau and C.V. Walker.