1622

THEORY AND PRACTICE OF ENGINEERING.

Book IL

buttresses outside 8 feet 2 inches.The cathedral or duomo at Pisa presents a very different result;the total width of the nave is113 feet 6 inches, and the widthof a severy 17 feet 1 inch, thearea of which is nearly 1930 feet,the points of support being only atwelfth of that quantity on theplan, and one-sixth as regardedupon the section. Hence we seethe necessity of ascertaining theproportions of mass and void in abuilding, before we can accuratelyjudge of its merits as a style, eachhaving its peculiar quantity, whichmarks its character.

The section or rather plan ofthe walls, ou the level with thegallery of the triforium, showsthe method adopted to proportionthe openings to the mass. Thethickness of the clerestory walls isincluded within the eight equila-teral triangles, and where theirsides cross, the position of themullions is established. In fig.3019. the circle which comprisesthe two that divide the windowinto three days shows their pro-portion and their size, whichin this example is one-tliirdof the opening: in a windowof three days we have six trianglesfor space, and three for mullions :the splays at the sides of thesewindows, uniting them withthe faces of the wall, are cutparallel with the sides of theseveral triangles. The main pieris set out by uniting the bases oftwo equilateral triangles withperpendicular lines, or formingthe whole into the figure of ahexagon. By a comparison ofthis plan with that of fig. 2999.,the additions made by William ofWykeham to the original Saxonpillar will be readily perceived.

The width of one of the di-visions of the nave at Winchester,measured from the centres of thepiers from west to east, is 22 feet1 inch, and the same dimensiontaken in the nave at Canterburyis 20 feet only. In the formerexample the opening between thepiers is 12 feet 1 inch, and in thelatter 14 feet; there is conse-quently no comparison, with re-gard to lightness, in these twoworks of the same period; the

Fig. 3035. PIER, AND WINDOWS OF CLERESTORY.

pier being comprised 2§ times in the entire division at Winchester, and 3^ times at Can-terbury, or on the pavement the plinths around the base seem to fall within one-third of theentire width. It would almost appear that in setting out the pillars of several cathedrals,the same system was practised as shown for the mullions of windows at fig. 8019. : but theplinths, and not the cluster of columns and mouldings, must be regarded as occupying thethird. Bath Abbey church is 20 feet 2 inches from centre to centre of pier from east to