Account of a series of observations, made in the summer of the year 1825, for the purpose of determining the difference of Meridians of the Royal Observatories of Greenwich and Paris

The operations, of which this paper contains an account, were undertaken by the British Board of Longitude, in conjunction with the French Ministry of War, at the invitation of the latter, for the purpose of connecting the Royal Observatories of Greenwich and Paris, by means of signals contemporaneously observed along a chain of stations established for that purpose between them. The signals employed were the explosions of proper quantities of gunpowder, elevated to a great height in the air by rockets fired at three stations, two on the French, and one on the English side of the Channel, and observed at the observatories, and at two stations intermediate between those at which they were fixed. These two stations were Lignieres on the French, and Fairlight Down, near Hastings, on the English side. The operations at the former were made by Captain Sabine and Colonel Bonne; those at the latter by Mr. Herschel and Mr. Largeteau; thus securing two independent lines of communication, a British and a French, between the extreme stations, and observers at each station exchanging observations at the termination of the whole operation, which was continued for twelve nights, ten signals being made at each station per night; and though the whole of them could not be employed, it is stated that the final result, which makes the difference of longitude between the two observatories equal to 9' 21".6, is not very likely to be found one tenth of a second in error, and extremely unlikely to prove erroneous to twice that amount. The observations are then stated in detail; and the mode of combining them in the most impartial manner, so as to deduce from them the most advantageous result, is next investigated; and a general formula deduced applicable to all operations of the kind, and including all the necessary corrections. This formula is then applied to the actual observations, and the result above mentioned deduced. The two results deduced by considering separately the observations of the British and of the French observers, at the intermediate stations, exhibit a remarkable coincidence,—their difference amounting to only a single hundredth of a second.