1826.] Philosophical Transactions for IS26, Parts Land 1/. 139 



their greatest altitude, was to constitute the signals to be 

 observed. 



''Our previous arrangements being made, on the 7th of July 

 I left London ; and after visiting the station pitched upon at 

 Wrothara, which was the same with that selected by Captain 

 Kater and Major Colby, as a principal point in their triangulation 

 in 1822 ; and finding it possessed of every requisite qualifica- 

 tion for the purpose of making the signals, from its commanding 

 situation, being unquestionably the highest ground between 

 Greenwich and the coast, proceeded to Fairlight Down, near 

 Hastings, where I caused the very convenient observatory tent, 

 belonging to the Board of Longitude, to be pitched immediately 

 over the centre of the station of 1821, which was readily found 

 from the effectual methods adopted by the gentlemen who con- 

 ducted the trigonometrical operations in that year, for securing 

 this valuable point. Here, on the 8th, I was joined by Captain 

 Sabine, who, it had been arranged, should proceed to the first 

 observing station on the French side of the Channel, there to 

 observe, in conjunction with Colonel Bonne, the signals made 

 on the French coast, and those made at the station of Mont 

 Javoult ; which latter were to be observed immediately from the 

 observatory at Paris; while, on the other hand, it was agreed 

 that M. le Lieutenant Largeteau, of the French corps of geo- 

 graphical engineers, should attend at Fairlight, on the part of 

 the French commission, and observe, conjointly with myself, 

 the signals made at La Canche, the post on the opposite coast 

 (elevated about 600 feet above the sea, being nearly the level of 

 Fairlight Down) and also those to be fired from Wrotham Hill, 

 which were expected to be immediately visible from a scaffold, 

 raised for the purpose on the roof of the Royal Observatory of 

 Greenwich. By this arrangement, and by immediate subse- 

 quent communication of the observations made at each station, 

 it was considered that the advantage of two independent lines 

 of connexion, a British and a French, would be secured between 

 the two extreme stations; i. e. the two national observatories; 

 every possibility of future misunderstanding obviated, and all 

 inconvenience on either side, arising from delay, or miscarriage 

 in the transmission of observations, be avoided. 



'* With the assistance of Captain Sabine, and by the help of 

 exact information as to the azimuths of Wrotham and other 

 nearer stations in the triangulation of 1821, with which Captain 

 Kater had obligingly furnished us, and of which Fairhght 

 Church proved the most convenient, being close at hand and 

 favorably situated, and easily visible in the twilight ; and from 

 the previously calculated azimuth of La Canche (114° 30' E.) ; 

 four night glasses by Dollond, provided at the order of the 

 Board of Longitude expressly for this operation, and which I 

 had caused to be fixed on posts firmly driven into the ground 



