Trigonometrical Survey. 531 
of triangles are in a north and south, or an east and west di- 
rection nearly, provided they are on, or near the meridian, or 
its perpendicular ; but if the triangles are considerably ex- 
tended, and in all directions, the bearings of the same stations 
(if they may be so termed) must evidently differ, and that 
sometimes considerably, when obtained from different tri- 
angles. To avoid, in a great measure, the errors which might 
affect the conclusions derived from the present triangles, if all 
those distances were determined from the meridian of Green- 
wich only, we have considered the meridians of Beachy Head 
and Dunnose as first meridians also, and, with two or three 
exceptions, calculated the distance of each station from its 
nearest meridian. Bagshot Heath, Leith Hill, Ditchling Bea- 
con, and Beachy Head, with those to the eastward, are from 
the meridian of Greenwich and its perpendicular; Chancton- 
bury Ring from the meridian of Beachy Head; and the others 
to the westward, from that of Dunnose. 
The advantages in this mode of proceeding are very obvious; 
for if the directions of meridians are taken at about 80 miles 
distance from each other, near the southern coast, the opera- 
tion may be extended to the Land's End with sufficient accu- 
racy, without making astronomical observations for determin- 
ing any intermediate latitude, as a new point of departure. 
In deducing the bearings of the several stations from the 
meridians and their perpendiculars, we have taken the observed 
angles, instead of those formed by the chords, which were used 
in computing the sides of the principal triangles ; because the 
latter angles at each station may be considered as constituting 
the vertex of a pyramid, and consequently their sum is less 
than 360°; but the operation of determining the distances 
