Trigonometrical Survey. 447 
by any former one, it was considered as proper to determine 
them with our own instrument. 
By a reference to the Philosophical Transactions, (Vol. 
LXXX. p. 162.) it will be found, that General Roy was obliged 
to elevate the instrument at the extremities of the base ; for 
which purpose a stage of thirty-two feet high had been con- 
structed. The same necessity existing with 11s, an application 
was made to the Royal Society for it ; and in the autumn of 
1791, that part of it which had been left at Dover, was brought 
to the Tower. 
The first station to which the instrument was taken this 
year was Hanger Hill, because it w 7 as found upon examination, 
that the part of the stage which had been left at Shepperton 
was much damaged, and stood in need of considerable repair. 
It was, however, soon fitted for use, and a new tent for the 
top having been provided, the half stage was erected over the 
pipe at St. Ann's Hill, to which from Hanger Hill the instru- 
ment was conveyed. Here, as* well as at the other stations 
where the stage was used, a plumb-line was let fall from the 
axis of the instrument over the point marking the station, 
being sheltered from the wind by a wooden trough. In the 
use of the half stage, the instrument was sufficiently steady 
when the wind blew moderately ; but from the crazy state of 
the lower part, it was only by watching for moments particu- 
larly calm, that satisfactory observations could be made when 
the whole of it was used. 
The following obervations will sufficiently explain the de- 
tail of this year's operations, which are given in the order of 
time in which they were made. By an examination of them it 
will be perceived, that most of the angles have been observed 
3 M 2 
