Trigonometrical Survey. 
487 
Hence the sum is the height of the beginning of 
the first chain above the end of the last, namely, 429,48 
But the handle of the chain at Beacon Hill was v 
6,7 feet above the stone, and at the other end it was 
1,3 feet ; therefore their difference is 5,4 feet, which 
subtract - - - - 5,4 
Hence the surface of the stone at Beacon Hill is 
higher than the surface of the stone at Old Sarum. 424,08 
art. v. Conclusion of this Section. 
When this situation was first examined, and selected for the 
measurement, it was imagined that one of the extremities of 
the base would be fixed on somewhere near the southernmost 
clump of fir trees, not far from the Amesbury road, because 
from that spot Highclere can be seen. Those trees are near 
the 52d hypotenuse, and therefore about a mile from Beacon 
Hill ; consequently, if that situation had been fixed on, the 
base would have been no more than six miles, and the correc- 
tion for the reduction of the hypotenuses to the plane of the 
horizon only about 16 feet. 
Now, although we think that the fixing on Beacon Hill 
as the northern extremity, is justified from the circumstance of 
a mile being added to the base, which is conceived to be more 
than a counterbalance for any errors which may arise from 
measuring down the side of a hill ; there were other reasons 
which made it proper ; a principal one is, that by selecting 
that spot, the base can be applied as a test to the triangles, 
without making the connection by means of several small 
ones ; and another is, that if a place near the trees had been 
fixed on, a station must afterwards have been chosen on Beacon 
3 R 2 
