8o Mr. Herschel's account of a series of observations 



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 opera- 

 tion, and which I had caused to be fixed on posts firmly 

 driven into the ground beneath the tent, were then pointed, 

 two on the station of La Canche, and two on that of Wrotham 

 Hill. Those directed to the former were of four inches clear 

 aperture, the others of three. In case of any difficulty arising 

 as to the pointing, I had taken care to provide myself with 

 an excellent eight-inch repeating theodolite, on the Reich- 

 ENBACH construction, by Schenck, of Berne ; but it was found 

 unnecessary to use it, as the night glasses were purposely 

 constructed with an azimuthal motion, and a rough gradua- 

 tion read off by an adjustable vernier, so as to allow their 

 being set at once a few minutes before the observations com- 

 menced, by taking Fairlight steeple as a zero point ; a cir- 

 cumstance which proved exceedingly convenient, as it allowed 

 of their being dismounted after each night's observations, 

 and removed to a place of security ; and thus rendering it 

 unnecessary to harass our small party by keeping guard in 

 our absence. 



On the night of the 8th I had directed blue lights to be 

 fired at Wrotham, as a trial of the visibility of the stations, 

 or rather as a verification of the pointing of the telescopes ; 

 for on the former point there could be no doubt, the station 

 at Wrotham being situated precisely on the edge of the 

 escarpment of the chalk which borders the Weald of Kent, 

 and having been actually connected with Fairlight by direct 

 observation, while no obstacle but a low copse wood, over 

 which it might fairly be presumed that no rocket would 



