140 Dr Pearson, On a neio hind of self-acting weir. [Feb. 25, 



the bed of the stream, and this was effected as follows : Each pair 

 of staunchions supporting a valve was maintained in an upright 

 position by means of an iron support forked at the upper end, 

 about four inches in diameter and eight feet long, resting at an 

 angle of about SS'* to the horizon against a ledge in the apron 

 of the weir : this ledge makes an angle of about 3" or 4" with the 

 vertical : and a long bar with claws attached, working in a stone 

 groove diagonal to the stream, is so placed to run under the ends 

 of all the supports (called in French^ arc-boutants) that it can lift 

 them one after another over the ledge : they then slide down on 

 the apron of the weir, and the valves, supports, and staunchions, 

 all assume nearly a horizontal position. The bar rests at either end 

 in a chamber at the side of the stream, and is worked by means 

 of cog-wheels and a windlass. When the flood has passed away, 

 the weir can be easily raised again by drawing the whole up- 

 stream by means of a chain or rope attached to the foot of each 

 valve successively, and working on a windlass placed in a boat 

 moored above : when the end of the iron support reaches the 

 ledge, it catches there, while the staunchions are by that time in 

 an upright position, and the lower end of the valve, the chain on 

 the windlass being relaxed, is pressed by the current into its 

 original place. The plan had the ostensible advantages of per- 

 mitting a rise in the river to open the weir of itself, and making 

 the weir itself practically removeable in a few minutes : and these 

 theoretical merits in no way disappear entirely, under the modifi- 

 cations which it has been found advisable to apply to the plan 

 where carried out in practice. 



As a matter of fact, the method was employed by M. Chanoine 

 from the first in two different ways. Recognising the great 

 obstacle tha,t a solid weir of any kind in a river is to the discharge 

 of a flood, he divided the weir erected by him at Conflans (near 

 Montereau on the Upper Seine) into two parts. Besides making 

 a lock of the usual kind adjoining the bank, he formed the river bed, 

 as M. Poiree had done, into two sections : in one, about 40 yards 

 broad, he constructed the apron of the weir in the bed of the 

 stream : in the other part, separated from the first by a buttress 

 of masonry, he placed the moveable framework on the top of a 

 solid weir of rubble-work, diminishing of course the size of the 

 staunchions and valves considerably: in the first section, which he 

 designed for the passage of vessels when the river was high, he 

 made the valves of the full length, in the other they were not more 

 than six feet long and the staunchions and supports of course 

 smaller in proportion. The valves also in the first portion, having 

 their hinges at a distance of about five-twelfths of the distance 



1 Arc-houtant means, in arcliitecture, a, flying-buttress: it is also used metaphori- 

 cally as e. g. V arc-houtant de Vetat, 



