CANAL CONSTRUCTION. 77 



(4) by being placed upon the same axle, and also con- 

 ne(5ted with a triangular brace (5). 



At the end and between the top levers (4) is sus- 

 pended upon an axle a weight box (W), in which is 

 placed rocks or other heavy material to counterpoise 

 the pressure of water in the canal against the surface 

 of the gate. When the water pressure becomes greater 

 than the counterpoise by reason of increased depth of 

 water in the canal, the gate swings open in an outward 

 dire6lion from the canal, and levers 3 and 4 are forced 

 back till the weight box goes past the center or per- 

 pendicular over the main axle just enough so as to 

 nearly counterbalance the weight of the gate and levers 

 I and 2, so that the gate is floating loose on the surf ace 

 of the freely escaping water with nothing to obstruent 

 it, and no opportunity for drift or silt > to lodge. The 

 gate is turned open to its full capacity and stands 

 nearly at right angles to its position when shut. As 

 soon as the flood has receded and the water in the 

 canal has lowered to its normal stage, the gate lowers 

 accordingly, when the weight is moved forward and 

 receives its former power and closes the gate. 



The forces a(5ling through the system of levers as 

 arranged, and holding the gate shut when the water in 

 the canal is at normal hight, or not exceeding the 

 hight to which the gate has been adjusted, are reduced 

 in the same proportion as the water pressure against the 

 gate is reduced when opened. Between each set of 

 gates is placed a beam or cap lengthwise of the waste- 

 way, supported on posts to which are fastened the box- 

 ings in which the main axle revolves. This axle is made 

 from timber six inches square, banded at each end, and 



