394
EXPOSITION AT VIENNA.
general demolition following the close of the Exhibition. It is composed entirely of iron, is circular in form, and covers, with its roof, the largest area as yet built over without the use of interior columns or pillars. Its essential features are thirty-two iron columns, placed at equal intervals in a circle, upon foundations of beton, and which support as many iron beams radiating towards the centre of the circle. A ring, also of iron, connects the tops of the columns and takes up the thrust of the roof, formed of iron plates riveted to these beams. The roof is of conical form, and supports a large and a small lantern. The diameter of the circle is one hundred and eight metres, and the height of the whole eighty- four metres. Exterior to the columns is a brick wall supporting an iron roof and inclosing the whole. The emperor’s pavilion is chiefly remarkable from the magnificence of the interior decorations, but has been lost to most of the visitors at the Exhibition, from the difficulty of obtaining entrance. Beyond these, an Austrian building, composed entirely of concrete, is worthy of note. The roof is vaulted of this material, and is above flat and surrounded by a balustrade. It serves the purpose of a terrace, and is reached by a stairway of concrete alone, and supported entirely by a single arch. It is claimed in Vienna that such buildings can be erected at a less cost than those of brick; but the difference appears slight, since the walls must be made somewhat thicker of concrete, and, where it is used in such masses, great care must be taken to prevent its cracking, and, consequently, crumbling. The experiment is an old one ; and, at the Exhibition in Paris in 1867, various laborers’ cottages were built of the material without seeming to meet with general favor. The English exhibitors have erected, at the present Exhibition, several cottages of corrugated iron nailed to a wooden frame. These have the merit of cheapness, but are of little value in excluding heat or cold. During; the hottest part of the summer it was excessively uncomfortable in their interior, and, moreover, in one or two cases where they have taken fire, elsewhere, they have burned like tinder. Wood in connection with iron, for building purposes, is, in fact, more dangerous than wood alone. When the latter has reached a glowing heat, everything in its vicinity that is at