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I, I, i ~ ~ ...... " ~."... u p U ~l P T E 5 Tl N G 53 il ~; I the motor and pump in cycles per second with a known constant speed source controlled by a carefully standardized tuning fork. The difference betwecn the speed of the pump and the standard constant speed is shown on the illuminated face of the instrument by a series of waves traveling across it. If the wave stands still it indicates that the frequency or speed of the motor is exactly the same as the frequency of the constant speed source. Waves progressing. in one direction show that the motor is running at a higher speed, and progress in the opposite di recti on indicates a lower speed. A mechanical counter registers the number of waves that pass in a given time and with this information the speed of the motor and pump in revolutions per minute can be accurately calculated. Measurement of speed is important because the guar'an- tees of pump capacity and power are made for a certain definite speed and if the speed during a test is even slightly more or less, appropriate correction must be made. The head. or pressure against which the pump lifted the water, was measured by mercury columns and by pressure gages which were carefully calibrated against known weights. The pumps all being submerged below the inlet water level, there is always a positive pressure on the pump inlet and the difference between the inlet pressure and the discharge pressure is the net pressure or head. It is somewhat greater than the actual height that the water is lifted on account of the friction losses in the inlet and delivery pipes. The quantity of water discharged by each pump was measured by the salt velocity method. This method was devised and devel- oped by Professor C. IV!. Allen, head of the department of mechani- cal engineering at Worcester Polytechnic Institute,_in .Massachu,. ._ --setfs~ alia-is gOllei'a]ly consi~l~r-;'d by. hydr~~lic -e;,gineers to be one of the most accurate methods that C,lll be used in measuring large volumes of water flowing in pipes. It is based on the principle that if a concentrated solution of common salt is injected into water, the electrical conductivity of the water is thereby increased. Two electrodes are placed in the pump discharge pipe a known distance apart, and connected to an ammeter which records on a rapidly moving chart the conductivity of the water as it passes the elec- trodes. Concentrated brine is injected into the pipe a short distance ahead of the electrodes, and as this quick "shot" of brine passes each electt'ode, its increased conductivity makes a "hump" in the otherwise straight line on the chart. Time, in seconds, is also marked on the chart by an accurate clock, so that the distance between the