1878.] Dr Pearson, On a netu kind of self-acting weir. 141 



from the bottom, were made so as not to rotate of themselves 

 except in an extreme case, while in the other part, they were so 

 balanced as to be nearly or quite self-acting. A full description of 

 the practical working of this weir when first erected, in Sept. 1860, 

 will be found in the Ann. des Fonts et Gltaussees for the following 

 year, p. 334; from which it appears that the two divisioDs at 

 Confians are respectively 40 and 28 yards in length : that in the 

 larger section, viz. that designed for the passage of vessels, the 

 framework could be lowered entirely in less than two minutes, 

 and restored to its upright position in less than an hour : while 

 the valves surmounting the solid weir, in this case only about four 

 feet and a half in height, were found to open or close according as 

 the water rose or fell in the river above them ; in opening they 

 were allowed to act of themselves, but having a counterpoise 

 attached to the lower end, which mov'ed higher up the valve when 

 the latter tended to become horizontal, they only returned to their 

 original position as the water fell, by the aid of a workman who 

 crossed the weir and pushed back the counterpoises, one after 

 another, to the lower end of the valve. 



Though it is stated that at first the sm.aller, self-acting valves 

 surmounting the solid weir, operated perfectly well, yet for various 

 practical reasons they have generally been so altered, as to be 

 raised or lowered by means of chains attaching each end of the 

 valves to a moveable windlass running on a truck along a light 

 bridge, corresponding to that employed in M, Poiree's system. In 

 fact it seems that M. Chanoine's original system, as explained by 

 him in the Ann. des P. et G. 1859, 1861, has partially been 

 modified, as has been found necessary for practical success : at the 

 same time his original theory is still retained, and his application 

 of it in the construction of that part of the weir, which is designed 

 to maintain rather than to regulate the level of the upper water, is 

 found to work perfectly well. 



The entire theory of the subject, as worked out by M. Chanoine, 

 will be found in a long article in the vol. of the Ann. des P. et G. 

 for 1861. In the vol. for 1873, there will be found a full de- 

 scription of the weir at Port a I'Anglais on the Seine, about 3 miles 

 above Paris, immediately above the junction of the rivers Seine 

 and Marne : this weir, originally erected about 1860, was consider- 

 ably altered in 1869, and in its present form it represents the 

 system as adapted to the requirements of a large traffic, and 

 including the various modifications suggested by an experience of 

 several years. Any one desirous of thoroughly understanding the 

 subject, should refer to the papers I have already cited and others 

 in the same series, especially one in the vol. for 1866, the plans 

 annexed are extremely elaborate, and explain the construction 

 down to the minutest details. Persons who wish to see the system 



