over Churches and similar Spaces. 233 



of eggshells. In the vaulting of the Minster at Ulm *, the tile 

 materials are known to have been mixed up with chopped 

 straw, which, in the burning, naturally was reduced to ashes, 

 and thus gave to the stone a degree of porosity, and conse- 

 quently of lightness. 



The author found the same thing in the church at Kirch- 

 berg, near Zimmern ; but he observed that here, in an expe- 

 riment made with different mixtures, tiles of this kind lose very 

 much in strength, which, for such vaults, is far more injurious 

 than the small excess of weight of common solid stone would 

 be ; even the latter does not amount to half the weight of a 

 common grouting (filling-in of the inside of a wall) ; and, con- 

 sequently, operates rather advantageously, than prejudicially, 

 to the stability of a substantial building. 



We find this kind of vaulting applied also in domes ; in 

 which case the circle is divided by ribs into compartments, and 

 compounded of several flat rounds. Among others, the 

 author found in an old tower at Andernach, a domed vault, of 

 which the horizontal section forms, not a circle, but four shell- 

 shaped pieces of circles, which rest upon two edges, cutting 

 each other at right angles. When, in later times, the ribs 

 were multipled, and a network of various forms was extended 

 over the vault, the intermediate spaces were smaller, and 

 could consequently, with still more facility, be vaulted with 

 free-handed vaulting. 



The advantage of this kind of vaulting without centering 

 consists, not only in the very considerable saving of boarding, 

 and of the greatest part of the centering arches, but it gives 

 also a firmer vault ; since the settling takes place gradually 

 before the usual closing of the vault : indeed, the author 

 almost doubts, whether such thin vaults could be constructed 

 at all upon a boarded centering. Except this is supported by 

 scaffolding to an immoderate degree, the mere motion of the 

 labourers, in the course of the vaulting, must cause a perpetual 

 shaking, and, consequently, separations in the vault after it is 

 begun ; and even when the vault is brought to its closing, 

 and it is wished to loosen the centering, which is so extremely 



* Ilaffner, Description of the Minster at Ulm, p. 11. 



