. Un manuel des principes et de la pratique de la construction routière: Comprenant l'emplacement, la conruction, et l'amélioration des routes (communes, macadam, pavés, planches, etc.) et des chemins de fer . un pivot, qui est le centre d'un quadrant divisé en de-grees. Pour mesurer une pente, placez la barre dessus, et tournez le niveau jusqu'à ce que la bulle soit en son centre. Le relevé en haut du niveau indique l'inclinaison de la pente. Pour augmenter son portabiKty, le long bardbbles vers le haut sur une charnière en son milieu.* pour former les sommets des remblais, et les bot-toms des boutures, selon le pr désiré

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. A manual of the principles and practice of road-making: comprising the location, consruction, and improvement of roads (common, macadam, paved, plank, etc.) and rail-roads . a pivot, which is the centre of a quadrant divided into de-grees. To measure a slope, place the bar upon it, andturn the level till the bubble is in its centre. The read-ing at the top of the level will indicate the inclination ofthe slope. To increase its portabiKty, the long bardoubles up on a hinge in its middle.* To shape the tops of the embankments, and the bot-toms of the cuttings, in accordance with the desired pro-file of the road, attach, to the under side of a conimon Simms on Levelling, p. 96. MECHANICAL STRUCTURES. Fig. 88. 173. masons level, a triangle ABC, with its base and heightso proportioned as to correspond to the crowning of theroad ; 1 in 24 for example. Or, instead of the triangle, gauges of different lengths, moveable on thumb-screws, maybe made to project below the level, to proper depths.* 2. MECHANICAL STRUCTURES. Under this head are included the bridges, culverts, andother works of the mason and carpenter, which are re-quired for the purposes of the road. BRIDGES. The most simple and natural form of a bridge consistsof two timbers, laid across the stream, or opening, which isto be passed over, and covered with plank to form theroad-way. Walls should be built to support each end ofthe timbers, and are named the abutments. The widthof the opening which they cross is termed the stretch, orhay. The timbers themselves are the string-pieces.Their number and size must of course increase with thestretch. For a stretch of 16 feet, they should be about * Parnell, p. 261. 174 THE CONSTRUCTION OF ROADS. 15 i

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