VOLTAGE.--Water may be made to flow with greater or less force, or velocity, through a pipe, the degree of same depending upon the height of the water which supplies the pipe. So with electricity. It may pass over a wire with greater or less force under one condition than another. This force is called voltage. If we have a large pipe, a much greater quantity of water will flow through it than will pass through a small pipe, providing the pressure in each case is alike. This quantity in electricity is called _amperage_. In the case of water, a column 1" × 1", 28 inches in height, weighs 1 pound; so that if a pipe 1 inch square draws water from the bottom it flows with a pressure of 1 pound. If the pipe has a measurement of 2 square inches, double the quantity of water will flow therefrom, at the same pressure. AMPERAGE.--If, on the other hand, we have a pipe 1 inch square, and there is a depth of 56 inches of water in the reservoir, we shall get as much water from the reservoir as though we had a pipe of 2 square inches drawing water from a reservoir which is 28 inches deep. MEANING OF WATTS.--It is obvious, therefore, that if we multiply the height of the water in inches with the area of the pipe, we shall obtain a factor which will show how much water is flowing. Here are two examples: 1. 28 inches = height of the water in the reservoir. 2 square inches = size of the pipe. Multiply 28 × 2 = 56. 2. 56 = height of the water in the reservoir. 1 square inch = size of the pipe. Multiply 56 × 1 = 56. Thus the two problems are equal. A KILOWATT.--Now, in electricity, remembering that the height of the water corresponds with _voltage_ in electricity, and the size of the pipe with _amperage_, if we multiply volts by amperes, or amperes by volts, we get a result which is indicated by the term _watts_. One thousand of these watts make a kilowatt, and the latter is the standard of measurement by which a dynamo or motor is judged or rated. Thus, if we have 5 amperes and 110 volts, the result of multiplying them would be 550 watts, or 5 volts and 110 amperes would produce 550 watts. A STANDARD OF MEASUREMENT.--But with all this we must have some standard. A bushel measure is of a certain size, and a foot has a definite length, so in electricity there is a recognized force and quantity which are determined as follows: THE AMPERE STANDARD.--It is necessary, first, to determine what an ampere is. For this purpose a standard solution of nitrate of silver is used, and a current of electricity is passed through this solution. In doing so the current deposits silver at the rate of 0.001118 grains per second for each ampere.