386
EXPOSITION AT VIENNA.
then built up with a light brick wall, which has nothing but its own weight to support. The amount of material thus employed is much less than that required by the first mentioned method. The spherical vault referred to has almost entirely supplanted the groin in the newer buildings here, and is generally built for small widths, without the use of scaffolding ; but not till the completion of the roof of the building, as rain could prove very injurious to its stability. "The arch never sleeps ”; and where it does not abut upon a wall of sufficient strength to support its thrust, it should be tied together. All the exterior walls of buildings are, in Vienna, firmly bound together by two or more ties of iron passing through their entire length, at each story. When these are built into the masonry, and protected from contact with the air, they are not affected by rust. At the demolition of a house at least fifty years old, I have seen such ties taken out in perfect condition.
Before proceeding to the description of fire-proof stairways, one of which, at least, is required in every building in Vienna, I will give a translation of the more important building-laws here in force, as they contain much information on this subject, and will assist in making the preceding portion of this article more intelligible.
1. When the position of a building is such as to make it desirable, as a precaution against fire, the ground floor must be vaulted. In the attic, and in the first story, when the ground floor is not vaulted, the floors must be massive (as described), and a layer of dry mortar, sand or other incombustible matter, must separate the beams from the planking.
2. Stables and hay-lofts must have a fire-proof ceiling.
3. Rooms for storing fuel must be, in general, located in the cellar, and built of masonry. When they are in sheds of but one story, they must, in addition, have a fire-proof roof.
4. In every building fire-proof stairwa} 1 2 3 4 * * 7 s must communicate
from the attic to the cellar, and with every dwelling, by means
of fire-proof passages. (This implies, that the vestibule
should be also fire-proof; and it is, in fact, invariably vaulted, and has a flooring of stone or beton.) In buildings of great oxtent, there must be several such stairways, sufficient to