Mr. Thom on New Self'.acting Sluices. 103 



down freely within the cylinder EF ; and the weight of which 

 keeps the sluice BD shut by its connection with 



BKH, a chain fixed to the cylinder GH at H, thence pass- 

 ing over the pulley K, has its other end fixed to the sluice 

 BD at B. 



When the water in the canal, river, or pond, rises to the line 

 BC, it passes into the cylinder EF, at the small holes IIII ; 

 and this lessens the weight of cylinder GH so much, that the 

 pressure of the water in front of sluice BD throws it open. 

 When the water subsides, so as not to enter these holes, the 

 cylinder is emptied by the tube EL, and then the weight of the 

 cylinder GH shuts the sluice as before. The dimensions and 

 weight of this cylinder must of course correspond with the 

 weight of the column of water pressing upon the sluice BD. 

 An apparatus of this kind was first erected at Rothesay in 1817. 

 The dimensions of one of these are : — cylinder GH two feet 

 diameter, and two feet deep over all ; weight 500 lbs. * Cy- 

 linder EF five feet ten inches deep, two feet one inch diame- 

 ter inside : sluice BD four feet long and two feet deep. 



This sluice is here represented with the pivots on which it 

 turns at its under edge, but they may be placed either at the 

 upper or under edge, as circumstances render advisable. The 

 upper edge is also here represented on a level with high-wa- 

 ter mark, but if necessary, it may be placed any where be- 

 tween that and the bottom of the pond or aqueduct, or right 

 below, as on an aqueduct bridge, or similar situation. The 

 cylinders may also be placed on the outside of the dam or 

 embankment by having a pipe to communicate between them 

 and the water within ; but in whatever situation the sluice or 



• This weight is considerably more than necessary when the sluice is placed 

 with the pivots at its under, and the chain at its upper edge ; but it was cal- 

 culated to be powerful enough when the sluice was turned with the pivots at 

 its upper and the chain at its under edge, to which position it has since been 

 changed. 



Although the cylinder GH requires to be heavier to shut the sluice when 

 its pivots are at the top, yet, to pass the same quantity of water, it does not 

 require to move half so far as when they are at the bottom, and therefore the 

 cylinder EF may be made much shorter ; so that the cost in either case is near- 

 ly the same, or rather in favour of the pivots being at the top. In most 

 cases this last position is preferable ; there are instances, however, in which 

 the other is more advisable, such as in a river where wood, ice, or other bulky 

 substances may be expected to float occasionally on the surface ; but such 

 cases require a particular construction adapted to the circumstances. 



