over Churches and similar Spaces. 



sequently, by means of its own weight, in combination with 

 that of the roof, exercises a powerful pressure upon the pillars, 

 which is more than sufficient to give them the stability requi- 

 site to enable them to counteract the unequal push of light 

 vaults. The profile, Fig. 7, of the Church of the Jesuits in this 

 place (built in 1615) will make this clear, since here we have 

 the still more unfavourable case, in which the vaults are not 

 only very unequal, but their points of incidence are not oppo- 

 site each other, being at different heights ; and consequently 

 the whole push of the vault (which is not pointed, but semi- 

 circular) operates upon the pillar, which has no support on 

 the other side ; nor are the outer walls, though only two feet 

 seven inches thick, strengthened by any buttresses ; while the 

 side windows have a width of only six feet for the interme- 

 diate piers: perhaps one of the boldest constructions of a 

 vault which is known. See the plan of the vaulting, Fig. 8. 



Fig. 8. 



In reality, indeed, the push of such thin vaults is not any- 

 thing which we need fear, since, according to the formulae of 

 Bondelet, or even those of Belidor, piers are sufficient for them 

 which have a smaller thickness than that which is usual in the 

 outer walls of high and wide buildings. Hence the ribs and 

 the filling in behind of the spring of the vault arches, supply 

 all the advantages which Bondelet, with truth, attributes to 

 vaults, of which the flanks are filled in behind, and which 



