30 



GEOGEAPHICAL POSITIONS. 



WEST COAST OF FRANCE. 



Cap Ferret, Lighthouse ... 



Contis, Lighthouse 



Cap Breton, Lighthouse ... 

 Eiver Adoui', Outer Light 



Bayonne, Bridge 



Biarritz, Lighthouse 



Socoa, Harbour Light 



St. Jean de Luz, Jetty Lt.- 



house 



liAT. N. 



Lomj. w. 



VAB. 



WEST, 



1895. 



AUTH0RITIB8. 



44 38 30 

 44 5 45 

 43 39 20 

 43 31 36 

 43 29 40 

 43 29 38 

 43 23 44 



43 23 20 



14 50 

 19 

 26 40 



1 31 10 



28 10 

 33 

 40 50 



15 45 



1 40 5 



The French Hydeooraphio 



Surveys. 



NOTES. 



1. Paris. — The grand operations, in point of aoauracy, for the determination of the length 

 of the degrees of ihe meridian, have taken place since 1783. In that year a memorial was 

 transmitted by M. Cassini de Thury to the Right Hon. Charles James Fox, then Secretary 

 of State. This application caused the operations by General Roy, already explamed, 

 which afterwai'ds extended into a General Survey. This gentleman, in England, acted in 

 conjunction with Messrs. Cassini, Mechain, and Legendi-e, in France ; but it unfortunately 

 happened that the results of the two parties did not exactly agree — that af the British 

 bemg, for the difference of longitude, 2° 19' 51", while that of the French was 2° 20' 15". 



In order to deterraine this question, the subject was resumed in 1821, on the suggestion 

 of the French authorities. The operations were consequently repeated mider the direction 

 of commissioners, nominated respectively by the Academy of Sciences and the Royal 

 Society. An account of the operations and results were given in the " Transactions " of 

 the latter, and the determination was that 2° 20' 22" was the difference between the 

 meridians of Paris and Greenwich. It was also attempted, in 1825, by the respective 

 governments on a plan suggested, we believe, by the late Sir John Herschel, and Captain 

 (afterwards General Sir Edward) Sabine, and Colonel Bonne, of simultaneous observa- 

 tions of rocket signals at a chain of stations; but they failed on the French side, and the 

 result, 2° 20' 22", was not considered satisfactory. 



Notwithstandmg the immense labour and consummate skill employed in these measure- 

 ments, the results obtained were doubtful, and it was reserved for the private means of a 

 commercial association to make another attempt to settle the question by means of the 

 electric telegraph. The death of M. Arago delayed the French preparations which were 

 organized when M. le Verrier became Superintendent of the Paris Observatory, and 

 several thousand signals were transmitted in 1854, so many, in fact, that a large portion 

 were rejected, leaving 1,700, or nearly 2,000, which were thought imexceptionable. Each 

 observation was probably as accurate as the mean of all former observations, and the 

 means of all showed previous results to be in error nearly a second of time (a large 

 quantity in astronomy). 



The mean result of th«se electric observations was that the D. L. between Greenwich 

 and Paris Observatories is 9™ 20-63^ of time, or 2° 20' 9-45" in arc. Later observations, 

 however, place it in 2° 20' 15". 



We have been more diffuse, perhaps, than necessary on this point, but it is one of 

 the most important geodetical operations ever undertaken. 



