1878.] Dr Pearson, On a neiv hind of self-acting weir. 139 



masonry, and the portion of the river bed between this and the 

 opposite bank he closed with a solid weir running in a slanting 

 direction up the stream. The new weir properly so called was 

 placed in the space of 70 m. designed for the passage of barges. 

 It consisted of a framework of iron and wood, the staunchions 

 of which were furnished with hinges at the feet, so that they could 

 be lowered into the bed of the stream. The framework was closed 

 against the passage of water by means of narrow paddles or staves, 

 called aiguilles, having handles at the top, resting against the 

 framework itself in a nearly vertical position. These aiguilles were 

 of wood, 1| inches square, and 6 feet long, thus giving when 

 in their places, a depth of at least 5 feet above the weir. The 

 framework was so constructed that a space of about 30 yards could 

 readily be opened or closed in less than an hour : the rest of the 

 barrier was designed to remain upright, except in case of floods ^. 



About the year 1851, M. Chanoine, another engineer of the 

 same branch of the public service, was permitted to introduce 

 a new modification based on the plan of M. Poiree, but including a 

 completely different idea, viz. the employment of valves, rotating 

 on an axis under the action of the water. In M. Poiree's system, 

 there was a double row of staunchions running across the stream, 

 connected' at the top and bottom by iron bars, with their feet 

 moving on hinges, but falling, Avhen lowered, in a direction across 

 the stream. Another horizontal bar running near the top of 

 these staunchions supported the aiguilles : the upper row of bars 

 joining the staunchions also supported loose planks, forming a 

 kind of light bridge. In M. Chanoine's scheme, the staunchions 

 stood in pairs at intervals of about four feet, their hinges being so 

 placed that they would fall, when lowered, in the direction of the 

 stream : the staunchions supported valves or floodgates, about ten 

 feet high by four broad, turning on an axis placed at a distance of 

 not less than one third, but always less than one half of the whole 

 length of the valve above the cill of the weir, reckoning from the 

 lower end : and at or near such a point that if the water above 

 and below the weir was at its normal height, the lower end of the 

 valve would be pressed against the cill of the weir by the water 

 on the upper side : but that if the water rose much higher, the 

 pressure on the upper section would become greater than that on 

 the lower, make the valve itself rotate (or "basculer," whence the 

 inventor termed these valves hausses a bascule) and allow the 

 stream to flow freely through the aperture, the valve remaining in 

 a nearly horizontal position until the water of the river had again 

 subsided ; should there be a serious flood, the staunchions (or 

 chevalets) were so constructed as to admit of being lowered into 



^ A full description of this barrier, witli plates, &c., will be found in the 

 Annales des Fonts et Chaussees, \o\. ii. 1839. 



