443 
Trigonometrical Survey. 
was found to be destroyed ; but this was considered imma- 
terial in its consequence, as it would have been improper to 
have chosen it for a principal station, because the high ground 
near Warren Farm took off the view of Leith Hill. 
A disadvantage however, which seemed to result from this 
resolution of avoiding high buildings for stations, occurred in 
the difficulty which offered itself of proceeding from Hanger 
Hill and St. Ann's Hill, with a mean distance of that side as 
given by General Roy ; for the station chosen at the former 
place being on the ground, there was scarcely a possibility of 
erecting a staff at King's Arbour, sufficiently high to afford a 
view of its top from Hanger Hill : a quadrilateral therefore, si- 
milarly posited, could not be fixed on ; but as a proper sub- 
stitute, a station was chosen upon the elevated ground near 
Banstead, which was visible from St. Ann's Hill, King's Ar- 
bour, and Hanger Hill ; and this, together with St. Ann's Hill 
and Hanger Hill, formed two triangles, which would give the 
distance between St. Ann's Hill and Banstead, independent of 
each other. 
Upon the return of Captain Mudge and Mr. Dalby from 
their expedition, in which they had selected many of the prin- 
cipal stations, and, by examining the face of the country, had 
formed some judgment of the future disposition of the tri- 
angles, preparations were made for taking the field ; and the 
party which had been engaged in the measurement of the 
base, were ordered to be attached to the trigonometrical ope- 
ration. 
Little difficulty was found in determining upon the choice 
of the necessary apparatus. Lamps were constructed, by Mr. 
Howard of Old-street, which were afterwards found to equal 
