This drawing of a cloister from a photograph shows the correctness of our perspective, and the manner of applying it to practical work.
Fig. 239.
[ CXXXII]
The Low or Elliptical Arch
Let AB be the span of the arch and Oh its height. From centre O, with OA, or half the span, for radius, describe outer semicircle. From same centre and oh for radius describe the inner semicircle. Divide outer circle into a convenient number of parts, 1, 2, 3, &c., to which draw radii from centre O. From each division drop perpendiculars. Where the radii intersect the inner circle, as at gkmo, draw horizontals op, mn, kj, &c., and
through their intersections with the perpendiculars f, j, n, p, draw the curve of the flattened arch. Transfer this to the lower figure, and proceed to draw the tunnel. Note how the vanishing scale is formed on either side by horizontals ba, fe, &c., which enable us to make the distant arches similar to the near ones.