^o6 COTTAGE, FARM, AND VILLA ARCHITECTURE. 348 are used, the laths to which the plates are nailed are almost always of wood. We have, indeed, in Moscow, in 1814, seen iron rods substituted for wooden laths, and the sheets fastened to them by strong copper wire; but we do not think the practice general. The common mode of covering iron roofs in Russia is thus given in a late number of the Ite- perlory of Patent Invetitions, &c. : — " Siieet-iron coverings are now universally made use of on all new buildings in Petersburgh, Moscow, &c. In the case of a fire, no harm can come to a house from sparks falling on a roof of this description. The sheets of this iron covering, measure two feet four inches wide, by four feet eight inches long, and weigh twelve pounds and a half avoirdupois per sheet, or one pound five ounces each superficial square foot. When the sheets are on the roof, they measure only two feet wide by four feet in length : this is owing to the overlapping. They are first painted on both sides once ; and, when fixed on the roof, a second coat is given. The common colour is red ; but green paint, it is said, will stand twice the time. Small bits, or ears, are introduced into the laps, for nailing the plates to the two-inch square laths on which they are secured. It takes twelve sheets and a half to cover 100 feet, the weight of which is only 1.50 lbs. ; the cost only £ : s., or about 3d. per foot." {Sup. to Rep. of Fat. Inveti., 1832, vol. xiii. p. 409.) 420. Corrugated Iron Roofs are coinposed of sheet iron, impressed so as to present a surface of semicircular ridges, with intervening furrows, lengthwise of the sheet. By this means, the sheet, from a plain flat surface having no strength but from its tena- city, becomes a series of continued arches, abutting against each other, fig. 348 ; and the metal, by this new position, acquires strength also from its hardness. To give an idea of the strength acquired, it is ob- served by Walker, the inventor of this mode of preparing sheet iron, that " a single sheet of iron, so thin that it will not continue in a perpendicular position, will, after undergoing the process of corrugation, bear upwards of 700 lbs. weight, without bending in the least degree." Iron so furrowed will be preferable to common sheet iron for covering a flat roof; because the furrows will collect the water, and convey it more rapidly to the eaves : but this is a trifling advantage, scarcely worth mentioning, in comparison with others which follow. Suppose, that, in addition to furrowing a sheet lengthways, so as to give it the appearance of 349 fig. 349, it is also bent in one general curve in the direction of its length, so as to give it the appearance of fig. 350, we have then an arch of great strength, capable of serving as a roof, without rafters, or any description 350 of support, except at the eaves or abutments. It is evident that, the span of any roof being given, seg- ments of corrugated iron may be riveted together, so as to form such an arch as may b^ deemed proper for covering it. To every practical man, it will be further evident, that a roof of extraordinary span, say 100 351 feet, which could not be covered by one arch of corrugated iron v.ithout the aid of rafters, might be covered by two or three, all resting on, and tied together by, tie-rods, fig 351. Furtlier, that in the case of roofs of a still larger span, say 200 feet, a tie-rod might be combined with a trussed iron beam, fig. 352 ; by wliiclj « <2, Tie roi's. bb,&c.. Corrugated arches, each forty feet span. re. Segment rafter of wrought iron, supporting the tie rod and tlie root of corrugated arches under it, and kept steady and strong by the trussing, d d, &c.
