80 Mr. Herschel’s account of a series of observations 
from the previously calculated azimuth of La Canche 
(114 0 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 
