1878.] Dr Pearson, On a new kind of self-acting weir. 145 



hibits a cross section, with tlie plank bridge E resting on bars 

 joining tlie two staunchions: here the water L is nearly, but not 

 quite, up to the normal height when the weir is closed. This 

 sketch, as mentioned above, is only introduced, as representing the 

 system of moveable fermettes devised by M. Poirde, from which 

 M. Chanoine borrowed his idea of moveable chevalets, supporting 

 self-acting valves. 



Fig. 2. The valves, or hausses (Fig. 2. 1. A.) are of wood : 

 M. Chanoine made them for the navigable pass, of 10 feet high, by 

 four broad, with the axis at a distance of -^ from the bottom, 

 omitting the portion of the valve resting on the cill when upright: 

 when placed upon a solid or "tumbling" weir, the axis is lowered 

 to a point /^ths from the bottom, thus making the valves revolve 

 more easily; but on the other hand the valve itself is only from 4 to 6 

 feet high, while the breadth is a few inches greater than in the other 

 case. The weight of a full-sized valve immersed is about 2 cwt. 



The upright staunchions or chevalets {B.) are adjusted in size 

 and dimensions to the valves which they support; the weight 

 of each is about 1 cwt. 3 qrs. 



C.G. are the arc-houtants or supports. They are inclined at an 

 angle of about 53° to the vertical, and weigh about 2 cwt. 1 qr. 

 each. They rest against a ledge inclined at an angle of about 3° 

 to the vertical, called a heurtoir, and are easily lifted over it by 

 means of the claws of the 



D. Barre a talons, a long iron bar, weighing about 11 cwt, 

 lying in a groove beneath the ends of the arc-houtants, and turned 

 by a cogwheel, upright bar, and lever : the two bars working on 

 one another in a chamber in the abutment of masonry at the end 

 of the weir. The force exerted on the lever in working the up- 

 right bar, is about 20 lbs. 



E.E. are the fermettes, or upright iron staunchions sup- 

 porting F, a windlass running on a light tram, G; the windlass 

 Avorking the chains H.IT which raise or lower the valve, E.E. can 

 be lowered into the stream by means of their hinges at K.K, 

 L.L. represents the water when the stream is at its ordinary level. 



Fig. 2. 2. represents a transverse section of the valve, and 

 abutment adjoining. 



Fig. 3. represents the valve and its apparatus lowered into 

 the stream during a flood. In December, 1872, at Port a TAnglais, 

 on the Seine, the water rose about 19 ft. or nearly double the 

 height of the valves when upright, above the cill of the Aveir. 



Fig. 4. represents, not quite accurately, the method of raising 

 a valve and its supports, when the water in the river has fallen. 

 The constant pressure of a full-sized arc-houtant against its ledge, 

 when the stream is in its ordinary condition and the valves verti- 

 cal, being estimated at about 4 tons, the force to be exerted on 



