12’6 Gen. Roy’s Account of 
were placed, turned, and clamped on the ferrules, In all re- 
fpefts fimiiarly with thofe of the long kind. By infpedtion of 
the plate it will be feen, that each of them carried on its fur- 
face a brafs fcale of fix inches in length, divided into inches and 
quarters, and moveable in a Aide, either backwards or for- 
wards, by a finger- fcrew adapted to the right-hand end. 
The right-hand poft of each group is called the drawing - 
pof, becaufe the iron fixed on its top carries a fmail apparatus 
of brafs, which being connected with the flat iron rod and 
hooks formerly ufed at Hounflow Heath, for a like purpofe, 
lays hold of the rear handle of the chain, and draws it back 
until zero co-incides with the point of commencement. The 
left-hand poft in each group is called the weight -poji, becaufe 
it carried a brafs pulley, over which a weight of 28 lbs. was 
hung by a fmail rope attached to the hooks that laid hold of 
the front handle of the chain. This weight acting againft 
the force of the fcrew at the other end, the chain was thereby 
kept perfectly ftraight in the coffers, and conftantly in the fame 
degree of tenfion, until fome certain divifion (the neareft for 
inftance) of the fcale could be brought, by means of the fcrew, 
accurately to coincide with 100 feet at the front end. That 
divifion, whatever it might be, was of courfe regiftered in the 
field book of the operation, together with the true temperature 
of the chain, as (hewn by five thermometers, one being laid 
for that purpofe in each coffer, and fecured with white cloth 
from the fun’s rays, as cccafion might require. 
Fifteen coffers were always arranged on the ground at the 
fame time, comprehending a fpace of the bafe equal to the 
length of three chains or 100 yards. The extremities of the 
firft chain having been accurately transferred, in the manner 
above mentioned, to the brafs fcales on the tops of the central 
2 pofts, 
