Measurement of a fcafe on Hounflow-Heath. 44 1 
the ninety-eight feet of coffering, which was kept fo much 
fliort of the hundred feet, that its extreme parts might not reft 
upon, or even touch, the central ftands. To that on the left of 
the center was attached the apparatus for thefirftor zeroendof the 
chain ; and to that on the right of the center was attached the 
apparatus for the laft end of the chain. When the fecond 
chain length had been meafured off, the firft and fixth of the 
coffer ftands of the firft chain were moved forward to prepare 
for the third chain ; and the four remaining coffer ftands were 
raifed, until their furfaces came into the fame plane with the 
Hide ftands, for the reception of the giafs rods. The fpace by 
which thefe ftands were raifed was about three inches ; for fo' 
much higher was the furface of the interfoie or flooring of the 
coffers than the ftands which fupported them. 
The apparatus attached to the firft end of the chain, or that 
which ferved to pull it back to the point of commencement, 
while a weight continued fufpended at the farther end, con- 
fifts of two parts, as may be feen by referring to the left-hand 
fide of tab, XVII. Firft, a fmall wooden frame, fitted to flip 
on to the top of any one of the ordinary ftands, placed imme- 
diately to the left of that which fupports the handle. Secondly, 
a flat fteel rod, about two feet in length, wherein a number of 
holes are pierced, about an inch afunder, for the reception of 
a fteel pin placed in one of the holes, as beft fuits the diftance 
of the ftand from the handle. That end of the' fteel rod 
neareft to the end of the chain is formed into a fcrew about 
four inches in length, and it receives upon it a forked hook 
fitted to lay hold of the ftraight part of the handle of the chain. 
Within the forked hook there works a ftrong milled-beaded 
brafs nut, which afting upon the bottom of the fork, the chain 
is thereby pulled back, until the wire fufpending the plummet 
