568 FRENCH AECHITECTURE. Pakt n. outer mouldings of the circle. Those of the transepts are smaller, being only 33 ft. across the opening, but show a considerable advance in the art of tracery, which by the time they were executed was be- coming fni- l)etter understood. If space admitted, it would be easy to select examples to trace the progress of the invention between these early efforts and the almost perfect window that adorns the centre of the west front at Rheims (Woodcut No. 423) ; and again from this to that at Evreux (Woodcut No. 424). In the latter instance, the geometric forms have given way 421. West Window, Cbaitres. 422. Transejit Window, Cliartres. 423. West Window, liheims. -124. West Window, Kvreux. to the lace-work of flowing tracery, of which this is a ])leasing example. It is further remarkable in respect that all the parts of the tracery or mullions are of the same thickness, whereas it is usual in flowing or flamboyant tracery to introduce a considerable degree of subordination into the parts, dividing them into greater or smaller ribs, thus avoid- ing confusion and giving to the whole a constructive appearance which it otherwise would not possess. This is very apparent in such a window as that which adorns the west front of St. Ouen, at Rouen,
