Fig. 5.
It would appear that the obvious mechanical advantages it offered led at an early period, in the south of France, to the substitution of the pointed for the round arch in the great vault of churches of this construction; but I will suppose for the present the semicircle to be strictly adhered to. The great defect in such a church as I am supposing would be want of light in the nave from the absence of clerestory windows; and as such windows had been in use from the days of the earliest basilicas, this loss would be fully appreciated.
Fig. 6.
The first idea for obviating it was to lower the springing of the vault for the sake of bringing the thrust to bear upon a portion of the wall more capable of resisting it, and, by raising the nave relatively to its aisles, to obtain space for a range of small windows between the roof of the aisle and the springing of the main vault ([Fig. 6]). This, however, was a most unsatisfactory arrangement—it compromised the security of the structure, and gained but a very miserable range of lights.
