In the gasoline car provision is made whereby, through the change speed gears, the engine gets the benefit of the leverage, by reducing the speed of the axle, relative to the engine shaft, at first speed, and this enables the motor to pull the car up steep grades, or over difficult roads, which it would not be able to do if the relative rotations were the same as at high speed. ECONOMY IN USE OF CURRENT.--The same thing is necessary in the operation of the electric motor. The current must be so arranged that at certain periods it will be more effective than at others, and this effectiveness is generally wanted at times when the axles turn very slow, just the same as with the gasoline car. This economizes, and prevents the waste of current. It is accomplished by connecting up the cells in such a manner that they may give a large voltage and small amperage, or a low voltage and great amperage, and in doing so will not detract from the efficiency of the battery. SERIES AND PARALLEL.--The device resorted to, whereby this may be accomplished, is in the manner that the cells are connected up with each other. In a general way, it may be said that the _voltage_ has reference to the force, or pressure of the current, whereas _amperage_ is the quantity which flows over the wire. Each cell has a voltage of, approximately, one and a half volts, and it matters not how large the cell may be, the voltage is no more. The amperage, however, depends on the surface area of the plates comprising the active agents in the cell, so that each cell has, say one and a half volts, and ten, or twenty, or more amperes. If a number of such cells are connected up in one way the output may be represented in high amperage, or in high voltage. If we have a certain number of cells, which, when combined, give ten volts and hundred amperes, the result would be 10 × 100, equal to 1000 Watts. But they may also be so connected together that they will have an output of 100 amperes and 10 volts, the total of which is also 1000 Watts. Such a current would be put through the motor under ordinary running conditions, as a high driving power is not necessary. But suppose it is desired to have a high or strong driving power; then the force of all the volts is required, so that one hundred volts are used, and only ten amperes. THE CONNECTIONS.--This is brought about by connecting up the cells in _series_, or, in _multiple_ or in _parallel_. The series connection is where the cells are placed in a row, for instance, and are connected together so that the carbon plate of one cell is joined by a wire with the zinc plate of the other cell; or the positive plate of one is connected with the negative plate of the other, and so on.