230 



On a Mode of erecting liyht Faults 



distances from each other, or from the outer walls, are unequal, 

 as is the case in almost all churches, must have a certain 

 stability before they are vaulted over, since the push of the 

 surrounding vaults is unequal, and, consequently, they no 

 longer hold each other in equilibrium ; their push not being in 

 this case resolvable into a simple perpendicular pressure upon 

 the pillars. This, then, is the use of that massive wall which 

 is carried by the arches, and which binds the pillars together 

 in the direction of the length of the nave. This wall finds a 

 resistance to its ends 'in outer walls of suitable strength ; and 

 at its upper part sustains a great portion of the roof; and con- 

 Fig. 7. 



