[ THE XXV. CONCLVSION.]
When you haue any peece of the circumference of a circle assigned, howe you may make oute the whole circle agreynge therevnto.
First seeke out of the centre of that arche, according to the doctrine of the seuententh conclusion, and then setting one foote of your compas in the centre, and extending the other foot vnto the edge of the arche or peece of the circumference, it is easy to drawe the whole circle.
Example.
A peece of an olde pillar was found, like in forme to thys figure A.D.B. Now to knowe howe muche the cõpasse of the hole piller was, seing by this parte it appereth that it was round, thus shal you do. Make in a table the like draught of yt circũference by the self patrõ, vsing it as it wer a croked ruler.
Then make .iij. prickes in that arche line, as I haue made, C. D. and E. And then finde out the common centre to them all, as the .xvij. conclusion teacheth. And that cẽtre is here F, nowe settyng one foote of your compas in F, and the other in C. D, other in E, and so makyng a compasse, you haue youre whole intent.
[ THE XXVI. CONCLVSION.]
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.
