BULLETIN OF THE UNITED STATES FISH COMMISSION. 255 



Should it be desired, on the other hand, to admit water from the river 

 into the pond — at the proper levels — the relative positions and opera- 

 tions of the valves would, of course, be reversed. The outer valve should 

 then be raised so as to allow the water to enter the flume from the river; 

 and the inner valve should be lowered, in turn, to permit it to swing 

 with the current, and to close automatically with the cessation of its 

 flow. 



Figs. 4, 5, C, and 7 represent portions of the above considerably en- 

 larged for the purposes of a more detailed description. The flap- valve d y 

 which is here represented as being forced slightly open by the presence 

 of the inflowing current, is attached to the lower extremities of the long 

 strips or pieces g g g, arranged to slide upward through mortises in 

 the beam a. The latter, in turn, is provided at each end with trun- 



Fin. 6. 



nions fitting loosely into corresponding sockets in the uprights p p, by 

 which means the beam and its dependent parts are allowed to swing 

 readily in place, as indicated by the positions of the gate or valve in the 

 several diagrams. 



Another and fixed beam, indicated at /, serves as an additional sup- 

 port to the uprights _p p, and as the fulcrum of a lever by means of 

 which the gate maybe raised or lowered. "CC C" represent crib- 

 work, filled with stones, and sustaining in position the screens s s and 

 o o, which are arranged to slide in their respectitive grooves, similarly 

 to those already described. 



Fig. 7 is a flume or trunk of simpler design which may be constructed 



