If so be it that you haue an arche of suche greatnes, that your
squyre wyll not suffice therto, as the arche of a brydge or of a
house or window, then may you do this. Mete vnderneth the arch
where y^e midle of his cord wyl be, and ther set a mark. Then
take a long line with a plummet, and holde the line in suche a
place of the arch, that the plummet do hang iustely ouer the
middle of the corde, that you didde diuide before, and then the
line doth shewe you the middle of the arche.
[Illustration]
_Example._
The arch is A.D.B, of which I trye the midle thus. I draw a
corde from one syde to the other (as here is A.B,) which I
diuide in the middle in C. Then take I a line with a plummet
(that is D.E,) and so hold I the line that the plummet E, dooth
hange ouer C, And then I say that D. is the middle of the arche.
And to thentent that my plummet shall point the more iustely,
I doo make it sharpe at the nether ende, and so may I trust this
woorke for certaine.