Meafurcment of a Bafe on Houn flow- Heath. 403 
meafuring rods, but fomething deeper, and fitted as ufual with 
proper points and micrometer. The ftandard rod being now 
conftru&ed was laid on the {hop -board, ftrongly framed for 
the purpofe, and nearly level. To one fide of it, at the diftance 
of about twenty feet two inches from center to center, two 
ftrong bell- metal cocks were firmly fcrewed. Thefe cocks 
were about inches in length, three-eighths in thicknefs, 
ji and rofe above the ffem nearly two inches, fo as to be on the 
fame plane with the furface of the meafuring rods, when 
placed upon it. 
A large plank, cut from the New-England maft, upwards of 
i thirty feet long, nine or ten inches broad, and about three 
i inches thick, being fet edge-wife ill the fame room, on part of 
the ffands now ready for the operation, was, in that pofition, 
planed perfectly fmooth and ftraight. A filver wire being then 
ffretched very tight, along the middle of the plank, from one 
end to the other, fix fpaces of forty inches each were marked 
off by the fide of the wire, at which points feven brafs pins, 
about one-tenth of an inch in diameter, were driven into the 
wood, and their tops polifhed with the ffone. During the whole 
of this operation, and that which followed, the thermometer, 
lying by the fide of the brafs fcale, continued ffeadily at or very 
near 63°. 
A fine dot being now made on one of the extreme pins, and 
the filver wire being ftretched over the dot, and as near as pof- 
fible over the middle of the other pins, in which pofition it 
was made faff ; the extent of forty inches, taken with the 
utmoft care from the brafs fcale, was then marked off, by 
; placing one point of the beam-compafles in the dot, and with 
the other defcribing a Ihort faint arc on the furface of the fe- 
cond 
