4i 8 Major- (mineral Roy’s Account of the 
being drained back fo as to coincide with the point of com- 
mencement,. a fteel arrow was placed as erect as pofilble in the. 
femi-circuiar cavity of the brafs handle at the other end.. The- 
chain being then drawn on, till the cavity in the rear handle- 
could be applied to the firft arrow, a fecond was then placed in 
that of the front handle, and fo on until fix chain lengths were 
thus meafured off;, which terminating the firft hypothenufe, a 
beech picket, fomething more than an inch fquare, and about 
feven in length, with N° I. cut upon it, was driven into the 
ground, till its head was nearly level with the furface. It is 
however to be remarked, that the fixth arrow of each hypo- 
thenufe was conftantly left in the ground till the firft of the 
fucceeding one was placed, to avoid the error that would have 
©therwdfe arifen in applying the rear end of the chain to the 
picket inftead of the arrow. 
In this manner we proceeded on the 1 6th of June, and in 
the fpace of about three hours and a half, completed the firft 
meafurement of the fouth-eaft fe&ion of the bafe, comprehend- 
ing the thirteen hypothenufes between the flag-ftaff and ftation 
near Hanworth Summer-houfe, the diftance being 78 chains or 
7800. feet, making 2600 yards ; and the mean temperature of 
the air being 63°. 
On the fubfequent day this fedtion was re-meafured with 
equal care, when the total extent fell fhort of the thirteenth 
picket only five inches. And here it is to be obferved, that a 
, confiderable part of this difference probably arofe from the 
ftretching of the chain acrofs Wolfey River, at the fame time 
that the irregularities of the ground are greater in this than 
In either of the other two fedtions. The mean heat of this, 
day was 65°* 
The 
