Chap. -XXII.

TIMBER ROOFS.

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iron works, they are executed with great strength, lightness, and economy of metal: thesmall vertical and horizontal rods acting as ties are made of wrought-iron, and the principalrafters and struts, which incline at the same angle, are of cast-iron ; such a series of trianglesmay be extended over roofs of almost any span, if due allowance be always made for the ex-pansion and contraction of the metal.

Fig. 2142. is a design for a roof, in which iron and timber are combined: the vertical rodssuspend the tie-beam, and when tightly screwed up bring the ends of the struts home against

Fig. 2142.

the principals and tie-beam, forming a very strong truss; the purlins may be supportedby a truss similar to that in the under side of the figure, by which means the entire roof willbe braced in every direction.

Roof of the old Riding-house at Moscow -The Emperor Paul , whilst travelling through

Europe in the year 1781, saw at Darmstadt an extensive riding-house, and on his arrival atMoscow he commissioned bis engineers to construct a similar building. Rondelet, upon

rig. 2143. BOOK OF OLD RIDING-HOUSE AT MOSCOW, as IT WAS FORMERLY.

the authority of Kraft, has given the design for a building 1800 feet in length and 290 feetin width, the interior being 220 feet, which has been copied and often described in

works on carpentry, but it never existed except on paper. M. Betancour has furnished inBruvere’s work the design for the building erected at Moscow , which was commencedunder his direction in June, 1827, and completed in the short space of five months:this riding-house is 531 feet in length, and 1GO feet in width in the clear. The foundationswere dug 13 feet deep, the bricks were made on the spot, and the timber used in itsconstruction was brought from the neighbouring forest. The walls were built up to thelevel of the ground, 14 feet thick, and above were 8 feet 6 inches.

A scaffolding composed of 1500 posts was raised level with the tops of the walls, forthe purpose of supporting the chief timbers of the roofs. The principals were at first 19 feet

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