2 88 Gen. Roy’s Account of 
forty-five triangles, determin'd the relative fituation of every 
Ration with regard to thofe neareft adjacent to it, we are next 
to (hew, from thefe data y and the angles which Norwood and 
Severndroog Caftle make with the meridian of Greenwich 
Obfervatory, the fituation of each Ration with refpedl to that 
meridian, to its perpendicular, and alfo the direft or diagonal 
diflance with the bearing from the Obfervatory itfelf. Thefe 
various determinations are contained in the fix firR columns 
towards the left hand of the annexed table of refults, wherein 
the Rations are likewife diftinguifhed into two fets, as fituated 
to the weft ward or eaftward of Greenwich. 
By means of a fcaffold, perfeflly fimilar in principle to that 
formerly defcribed, but more flight as being made for the tem- 
porary purpofe only, the ftand of the inftrument was railed to 
the height of thirty-eight feet above the floor of the tranfit- 
room of the Obfervatory. At this elevation all the furround- 
ing objects which we wifhed to obferve (St. Paul’s excepted, 
which is hidden by the camera* turret of the great room) could 
be diftindtly feen, and the angles between them and the fouth 
meridian mark accurately meafured. As that mark is but at a 
fhort diftance, namely, about 1500 feet from the tranfit, and 
eonfequently _ J ^th* of an inch correfponding to about a fecond 
of an angle on the mark, it was therefore very neceflary that 
the center of the inftrument fhould be brought with great pre- 
clfion over the center of the axis of the tranfit-telefcope un- 
derneath. In this operation, and indeed in every other while 
at Greenwich, the Aftronomer Royal gave us his beft afliftance. 
In the firft place, the central point of the axis was determined 
by the interfe&ion of diagonal lines drawn acrofs the fquare 
pari in the middle. On this fquare part, when the telefcope 
was in its horizontal pofition, a bafon of quickfilver was 
placed, 
