THEORY AND PRACTICE OF ENGINEERING.
1614
Book II.
circles at this period ; these were the principal decorations after the Lancet style was aban-doned, and were continued until succeeded by more flowing and varied designs.
Rose Window of the South Transept at Beauvais , 34 feet 4 inches in diameter, is composedof six large circles and their intersections.
To set out this win-dow the great circleexpressed by the outerbead is divided intotwelve parts, eachbeing equal to half theradius; twelve equi-lateral triangles arethen inscribed, thepoints of which toucheach of the divisions,and where they crossnearest to the outer. circle, the twelvepointed arches thatsurround the figureare struck; the otherpoints of intersectionof the triangles arecentres, from whichthe other curves aredrawn. It must at oncebe evident, that in acircle so divided, or byany other equal num-ber of equilateral tri-angles, the portionscontained between thesmaller angles mustbe equal to each other;the six circles aroundthe centre have theircurves blended intothe outer, and if it berequired to fix centresfor each of these flow-ing lines, they can onlybe obtained by cover-ing the entire rosewindow with lines inthe manner alreadydescribed. The radiusbeing equal to theside of a hexagon, andthat figure being com-posed of two equi-lateral triangles, wasprobably the chiefreason of its first pre-ference over all others;it certainly affords themost extraordinarypowers of combination,
and there is carcely a moulding or form in the architecture of this period but is set outfrom it. The mullions that bound the divisions are all portions of this figure, as are themouldings, which sweep round the arches of the buildings themselves. Nothing can sur-pass the brilliant effect of these marigold windows when glazed with rich colours, andexposed to either a rising or setting sun ; in the example now described, this effect is stillfurther heightened by making nearly the whole end of the southern transept a continuationof the same design, the glass descending almost to the tops of the doors which afford accessto the cathedral. The construction of such works must excite our highest admiration, forit appears scarcely possible to excel the perfect manner in which the parts are puttogether and worked off, the execution being in every particular worthy the design.
Fig. 3023.