Though it stands quite alone in point of intricacy and magnificence, it is not the first instance of the use of the peculiar system on which it is founded. How Fuller could have attributed its origin to the foreign studies of the King and Bishop Fox, it is difficult to conceive; for, not only is fan groining itself a purely English invention, but the special system of this roof has, so far as I know, only English prototypes.
The earliest of these is the vaulting of the Divinity School at Oxford,[61] finished about 1480. This was subsequently imitated, though with the loss of its leading principle, in the choir of the Cathedral (then the Church of St. Fridewide’s Convent in the same city), a work which, though popularly attributed to Wolsey, is probably of earlier date.
I have often looked in vain for the leading principle on which this wonderful work was designed. Its construction is plain enough; the difficulty is the ideal of its design. Like everything, however, which is founded on reason, its idea once perceived, it becomes perfectly simple, and one then only wonders where the difficulty lay.
It was simply as follows:—First imagine, for argument’s sake, that the architect had intended to divide his space into three spans—a wide and two narrow ones—like the Lady Chapel at Salisbury, or the crypt of the Sainte Chapelle at Paris, supporting the vaulting on ranges of thin pillars ([Fig. 395]). The setting out of the divisions was about the following. The whole span being divided into five parts, two were given to the width of a bay, one to the imaginary aisle, and three to the central span. The vaulting of the aisles, then, would be in oblongs of double their width set lengthway of the building, and the central span in oblongs half as long again as their width set crossway to the building.
Fig. 395.
Let us apply to each the rule I have already laid down for the fan vaulting of oblongs. Beginning with the ideal aisles, from the pillars and responds and centres draw the lower circles of the fans reaching the apex of the narrower arches, and the upper circles reaching the apex of the wider arch ([Fig. 396]). This gives us an oblong fan vault in its most normal form.
