HALIFAX WATER WuHKS. — JOHX.STOX. 113 



The Ventnri meter is different in principle, (lesii>ii and opera- 

 tion from the water meters generally nsed for measuring water, 

 it consists of two truncated cones of cast-iron, joined at the 

 smallest diameter bv a short throat lined with brass having 

 a diameter varying in different meters from one-quarter to 

 one-half of the diameter of the large ends of the cones, tlu^ 

 three parts making what is known as the meter tube. At the 

 up-stream end and at the throat small holes are drilled into 

 the tube, from which pipes are carried to the register. The 

 oi>eration of the meter is due to the fact that when water is 

 flowing through the tube the pressure at the throat is less than 

 at the up-stream end, and that the difference in pressure is 

 depende.it upon the quantity of water flowing through the tube. 

 The differing pressures at the up-stream end and throat <.)f tin- 

 meter tube are transmitted through small pi])es to the register, 

 which can l)e located at any convenient ])oint within -300 to -100 

 feet of the tube. I.i the register the differences of pressure 

 affect a column of mercury which carries a float. The 

 position of the float is thus made de})endent upon the quantity 

 of water passing through the meter; and by suitable mechanism 

 the quantity is recorded by a counter, and the rate of flow at 

 intervals of ten minutes is recorded upon a chart, so that the 

 fluctuations in the flow throughoiit each day can be observed. 

 Although the pressure at the thmat nf the meter is often several 

 {X)unds less than at the inlet or up-stream end, the lost })re.-sure 

 is almost all regained by the time the water reaches the outlet 

 end of the tube, so that the net loss of i)ressure caused by the 

 meter is seldom more than one pound under ordinary con- 

 ditions of use. The meters in Halifax are set on a by-pass so 

 as not to interfere with the operation of the scraper in cleaning 

 the mains. 



As there has Ix^en no direct means of measuring the water 

 used it has had to be estimated by finding out the loss of 

 pressure by friction in the pipes by gauges placed on hydrants 

 at different points, and to estimate tlie co-efficient to use 



PitOf . & Trans. X. S. Inst. Sci.. Vni,. XII. Tr.\ns. 8. 



