39. NOTRE DAME DE PARIS. FLYING BUTTRESSES AND SOUTH TOWER
The naves of Sens and of Bourges are also vaulted in square compartments. The thrust of the vaults is carried by the diagonal arches to each alternate pier, the intermediate one receiving only the auxiliary transverse arch already fully described. Yet here again the exterior flying buttresses are all of equal solidity in spite of the varying strain. This arrangement, prudent if illogical, shows once more with what distrust architects had adopted that system of exterior abutment, the characteristic of which is a detached arch exposed to all the vicissitudes of weather, and yet responsible for the stability of the whole edifice.
The Cathedral of Sens marks a new phase of development by its suppression of the upper gallery over the side aisles. These are now vaulted and covered by a lean-to roof; a flying buttress of single span receives the thrust of the main vault. The building is perfectly solid; its construction shows research, though it is as illogical as that of Laon or of Paris; for the exterior flying buttresses are all of equal strength, and so fail to proclaim their true functions, the interior thrusts varying considerably.
40. SENS CATHEDRAL. PLAN OF A BAY. VAULT IN SQUARE COMPARTMENTS OF TWO BAYS
41. SENS CATHEDRAL. SECTION OF A BAY OF THE NAVE
42. SENS CATHEDRAL. INTERIOR VIEW OF LATERAL BAYS