LX. T. W. SEAVER. 



a vacuum iu the latter in which the water rose as the 

 velocity increased. 



For irrigation purposes it is however more convenient to 

 have some means by which a fixed quantity of water can 

 be delivered per minute, and to effect this object when the 

 head varies, many forms of modules have been used but so 

 far with but little success. The only one that at all meets 

 these requirements at present was designed by Mr. A. D. 

 Foot, c.e., whereby the head over the outlet orifice can be 

 maintained with some degree of certainty by means of a 

 long returning weir. A very simple and efficient form of 

 module was designed in India many years ago by Lieut. 

 Carroll, of which the following is a short description. Fig. 8 # 

 The mouth of the outlet pipe has a plate hanging in front 

 of it, to which is attached a quadrant which more or less 

 closes the waterway. At its highest position there is a 

 free get-away for the water underneath it and between 

 the lips of the outlet and hanging plate. If the velocity 

 be increased, this plate is forced outwards and the quadrant 

 descending into the tube decreases the flow. 



The following is a description of a simple module which 

 has been designed by the author (Fig. 7): — A gate free to 

 slide up and down in front of the outlet is suspended from 

 one end of a lever, the other end of which is attached to a 

 tank floating in the main channel. To adjust this apparatus, 

 close the gate down till the required discharge takes place 

 under any given head. Then keeping the chains from the 

 gate and tank stretched upwards, mark upon a board the 

 position of the lever. Repeat this, with various heads, 

 when a series of lines will be drawn on the board, mark- 

 ing the positions of the lever, draw a curve to which these 

 lines form tangents, and cut the board along it. If now 

 the lever rolls on this curve, the relation between the head 

 of water and the size of the outlet must always be such 

 that the discharge will be a constant quantity. 



