The figure on page 242 shows a magnetic compass needle. This is used to test the direction of an electric current flowing through a wire or cable conductor. The plus sign, +, is the positive and the minus, -, sign is the negative end or pole. _A continuous current always flows from the positive to the negative end or pole_, hence the north end or pole, N, is the positive end of the needle and the south pole, S, is the south pole of the needle. When one of these devices is held in close proximity to a conductor of electricity _it immediately assumes a parallel position to the conductor_ and indicates the direction in which the current is flowing. The long, upper arrow, as shown in the figure, tells the direction of the flow. A small pocket compass may be used in place of this device and is often carried in the pocket of electricians for the purpose of indicating the direction of the current. PRESSURE IS NECESSARY TO PRODUCE AN ELECTRIC CURRENT. It should be understood that an electric dynamo or battery does not generate electricity, for if it were only the quantity of electricity that is desired, there would be no use for machines, as the earth may be regarded as a vast reservoir of electricity, of infinite quantity. But electricity in quantity without pressure is useless, as in the case of air or water, we can get no power without pressure, a flow of current. As much air or water must flow into the pump or blower at one end, as flows out at the other. So it is with the dynamo; for proof that the current is not generated in the machine, we can measure the current flowing out through one wire, and in through the other—it will be found to be precisely the same. As in mechanics a pressure is necessary to produce a current of air, so in electrical phenomena an electro-motive force is necessary to produce a current of electricity. A current in either case can not exist without a pressure to produce it. ELECTRIC PUMPING MACHINERY. Since the conditions surrounding pumping plants are so widely different, it is impossible to treat every practical application in detail, hence, the space allotted to this subject has been used in the preceding succinct and plain discussion of the principles upon which electric power is applied to the operation of pumps. The following are some of the advantages claimed for electric pumping machinery: “Economy in operation and maintenance is the first and most vital consideration that demands the attention in the installation of pumping machinery. In respect to economy, the electric system has many important advantages. It is saving in the transmission of power, and thus enables a pumping installation to be situated at a considerable distance from the source of power where the first cost and maintenance expense of other systems would be almost prohibitive.