To finde the centre to any arche of a circle.
If so be it that you desire to find the centre by any other way
then by those .iij. prickes, consideryng that sometimes you can
not haue so much space in the thyng where the arche is drawen,
as should serue to make those .iiij. bowe lines, then shall you
do thus: Parte that arche line into two partes, equall other
vnequall, it maketh no force, and vnto ech portion draw a corde,
other a stringline. And then accordyng as you dyd in one arche
in the .xvi. conclusion, so doe in bothe those arches here, that
is to saie, deuide the arche in the middle, and also the corde,
and drawe then a line by those two deuisions, so then are you
sure that that line goeth by the centre. Afterward do lykewaies
with the other arche and his corde, and where those .ij. lines
do crosse, there is the centre, that you seke for.
_Example._
[Illustration]
The arche of the circle is A.B.C, vnto whiche I must seke a
centre, therfore firste I do deuide it into .ij. partes, the one
of them is A.B, and the other is B.C. Then doe I cut euery arche
in the middle, so is E. the middle of A.B, and G. is the middle
of B.C. Likewaies, I take the middle of their cordes, whiche I
mark with F. and H, settyng F. by E, and H. by G. Then drawe I a
line from E. to F, and from G. to H, and they do crosse in D,
wherefore saie I, that D. is the centre, that I seke for.