To find out the centre of any circle assigned.
Draw a corde or stryngline crosse the circle, then deuide into
.ij. equall partes, both that corde, and also the bowe line, or
arche line, that serueth to that corde, and from the prickes of
those diuisions, if you drawe an other line crosse the circle,
it must nedes passe by the centre. Therfore deuide that line in
the middle, and that middle pricke is the centre of the circle
proposed.
_Example._
[Illustration]
Let the circle be A.B.C.D, whose centre I shall seke. First
therfore I draw a corde crosse the circle, that is A.C. Then do
I deuide that corde in the middle, in E, and likewaies also do I
deuide his arche line A.B.C, in the middle, in the pointe B.
Afterward I drawe a line from B. to E, and so crosse the circle,
whiche line is B.D, in which line is the centre that I seeke
for. Therefore if I parte that line B.D, in the middle in to two
equall portions, that middle pricke (which here is F) is the
verye centre of the sayde circle that I seke. This conclusion
may other waies be wrought, as the moste part of conclusions
haue sondry formes of practise, and that is, by makinge thre
prickes in the circumference of the circle, at liberty where you
wyll, and then findinge the centre to those thre pricks, Which
worke bicause it serueth for sondry vses, I think meet to make
it a seuerall conclusion by it selfe.