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Proceedings of the British Association. 



leaves, so that the upper portions of them shall be of much greater 

 area than the lower. The upper leaf is also far larger than the lower, 

 and turns in the direction of the stream ; while the lower leaf turns 

 against the stream, and overlaps the bottom edge of the upper leaf, 

 and is forced against it by the pressure of the water. The comparative 

 area of the leaves and position of the pivots is so arranged, that in 

 ordinary states of the stream the tendency of the current to turn over 

 the top leaf is counterbalanced by the pressure of the water against the 

 overlap of the bottom one, the counteracting pressures keeping the 

 weir vertical and the leaves closed, the water flowing as usual through 

 a notch in the upper leaf. But when the water rises above the usual 

 level, the pressure above from greater surface and leverage, overcomes 

 the resistance below, and the top leaf turns over, pushing back the 

 lower leaf, and thereby offering the least possible obstruction to the 

 water, and giving a passage at the very bottom of the stream to 

 the gravel or mud. 



In answer to questions and objections, Mr. Bateman explained how 

 difficulties, arising from trees floating down, the complete turning over 

 of the leaves, &c, might be obviated by suitable stops, grating, &c. — 

 Sir J. Robison observed, that the Rotterdam Canal had weirs on a 

 similar principle ; but Mr. Bateman explained that those weirs turned 

 vertically on their axis. The following diagrams will explain the 

 construction of the weir : — 



Mr. Viguoles stated, that from the cheapness and apparent advan- 

 tages of this weir, he should bring it under the consideration of the 

 Commissioners of the Shannon Navigation, and recommend it for trial 

 on that river, to which it appeared peculiarly applicable. 



Mr. Liddell read a paper on Ventilation, on a method proposed by 

 Mr. Fleming of Glasgow. It had been tried in a large building occupi- 

 ed by a number of poor persons, each family having a room. From 

 the unclean and intemperate habits of the inmates, and their number 

 (about 500), the house was very unhealthy, and many deaths from 

 contagious diseases took place. In the plan adopted, the galleries 

 were traversed by pipes of nine inches diameter, which united in a 

 vertical pipe of large dimensions communicating with a lofty engine- 



