. An encyclopaedia of architecture, historical, theoretical, & practical. New ed., rev., portions rewritten, and with additions by Wyatt Papworth. hod of finding the shape of these is the same,whetlier for sustaining plastering or supporting the hoarding ofcentres for brick or stone work, except that, for plaster, the inneredge of the rib is cut to the form, and, in centering, the outeredge. Groins, as we have already seen, may be of equal or im-equal height, and in either case the angle rib may be straightor curved; and these conditions produce the varieties we areabout to consider. 2059. To
. An encyclopaedia of architecture, historical, theoretical, & practical. New ed., rev., portions rewritten, and with additions by Wyatt Papworth. hod of finding the shape of these is the same,whetlier for sustaining plastering or supporting the hoarding ofcentres for brick or stone work, except that, for plaster, the inneredge of the rib is cut to the form, and, in centering, the outeredge. Groins, as we have already seen, may be of equal or im-equal height, and in either case the angle rib may be straightor curved; and these conditions produce the varieties we areabout to consider. 2059. To describe the parts of a groin jv/icre the arches are cir-ciihir and of unequal height, commonlg called Welsh (froins. Weliere supjiose the groin to be right-angled. Let AB (fg. 705.)be the width of tlie greater arch. Draw 1?D at right angles toA15, and in the straiglit line BD make CI) equal to the widthof the lesser arch. Draw DF and CE perpendicular to BD andEF parallel to BD. On AB describe the semicircle BghiA, andon EF describe tlie semicircle E^roF. Produce AB to p, andFE to m, cutting Ap in y. Through the centre x of the semi- atclii. Chap 111. CARPENTRY. 641
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