HALIFAX WATER WORKS. JOHNSTON. 113 



The Venturi meter is different in principle, design 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 by 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, the 

 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 

 operation 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 

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

 The differing pressures at the up-stream end and throat of the 

 meter tube are transmitted through small pipes to the register, 

 which can be located at any convenient point within 300 to 400 

 feet of the tube. Li the register the differences of pressure 

 affect a column of mercury which carries a float. The 

 position of the float is thus made dependent 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 throughout each day can bo observed. 

 Although the pressure at the throat of the meter is often several 

 pounds less than at the inlet or up-strearn .end, the lost pressure 

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

 end of the tube, so that the net loss of pressure 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 been 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 

 ni, different points, and to estimate the co-efficient to use 



PROO. & TRANS. N. S. INST. Sci., You XII. TRANS. 8. 



