Chap. XXXI.
PRINCIPLES OF PROPORTION.
1617
The North Rose Window at Amiens , 37 feet 8 inches in diameter, is a magnificent exampleof the application of the pentagon, with 5 isosceles triangles around it.
This window, probablyexecuted in the fourteenthcentury, has a great resem-blance to the last described;the fan tracery,' of whichwe have early specimens inthe cloisters at Gloucester,required the same know-ledge of geometry to perfecttheir design. In 1482Euclid was first printed atVenice from the Greektext; but geometry had beenstudied in England from thetime that Adhelard, in 1130,had introduced a transla-tion of that author fromthe Arabic versions whichhe met with during his tra-vels in Spain . In 1256Campanus of Navarretranslated Euclid , whoseems to have been com-mented upon by severaleminent writers, and nodoubt it was the text-bookof the freemasons, who dili-gently applied the problemsit contained to every pur-pose of their art. In 1486the Editio Princeps ofVitruvius appeared, andthe commentaries of CajsareCassariano followed in1521; the latter authorpublished three plates ofthe Cathedral at Milan,covered with equilateraltriangles, which have notbeen described so as to beuseful or understood.
The compartments whichhave the flat sides of the original pentagon for their base, and parallel sides throughout tillthey terminate in the pointed arch, have their mullions proportioned to their opening, thelarger being double the size oi the smaller, whilst the latter are equal to half the open spacebetween them : the mullions in these examples, which divide two spaces, 6 inches inwidth, are usually 3 inches in thickness, and the others are in the same proportion. Thenext sized mullion is 4^ inches, with a bead of 1^ inch diameter, which runs round thewhole pattern of the figure, the centre of which may be called the master line, by whichall the rest are set out; the several mullions are all twice as much in depth as in width.
Baptistery of Pisa . — The internal diameter of this circular building is 100 feet, and thethickness of its outer walls and columns 10 feet 6 inches ; its external diameter is 121 feet,the area of which is 11,499 superficial feet, that of the interior being 7854; if wededuct from it what is occupied by the four piers and eight columns, or 188 feet, wehave 7666 feet for the void, exactly two-thirds of the entire area. To find these pro-portions in an edifice commenced about the middle of the twelfth century in Italy , is acurious corroboration of the opinions already advanced, the same rules as those describedf or the Chapter House at Wells being apparently followed: the conical brick dome was theWork of an after period, and may have been the prototype for that of St. Paul’s at London ;the pointed architecture belonging to the exterior of this edifice, of the same character asthat which adorns the crosses of Queen Eleanor in England, was added in the fourteenthcentury.
The section shows how the equilateral triangle governs the proportions of this celebratedbuilding; the extreme diameter is the base, and its apex the level on which the
Fig. 3026.