4~J2 'Major-General Roy’s Account of the 
From the idart on the feather-edge coincides with the point of 
commencement on the ground underneath ; for which purpofe 
there is a hole in the top of the {land through which the wire 
pafles. The apparatus dand, thus ferving to pull back the 
chain, was commonly loaded with double Weights, placed on 
the two bindermod legs. 
The apparatus for the lad end of the chain Confids, like the 
Former* of a fmall wooden frame that can be readily flipped 
upon any of the common dands, as may be feen by referring 
to the right-hand lide of tab. XVII. This frame carries a 
pulley, over which a rope pafles having fourteen pounds weight 
fufpended at one end of it, while a forked iron hook at the 
other end lays hold of the ftraight part of the brafs handle. By 
means of thefe two apparatufes the chain is always kept to the 
fame degree of tendon in its coffers, in each of which a ther- 
mometer was placed to indicate the temperature ; the whole 
being covered Up from t'he diredt rays of the fun by a narrow 
piece of linen cloth, ftretched along it from one end to the other. 
Each coffer confided of three boards about half an inch, 
thick. The fides were about five inches deep, nailed at the 
middle to an interfoie bottom of four inches, in fuch manner 
as to be reprefented in fedion by the letter H. They were ill 
made, being by their parallelogram fhape apt to warp, which 
might have been prevented by giving them the figure of the 
cafes of the glafs rods, that is to fay, making them wide in the 
middle and narrow at each end. 
We are now to proceed to give fome account of the double 
rneaiurement with the chain and glafs rods ; wherein it mud be 
remembered, as alfo in continuing the operation with the glafs 
rods alone, that in referring to the map for the daily progrefs 
in the work, we are going from the forty-fixth towards the fird 
dation ; 
