[Illustration: FIG. 73.--Diagram of a multiple or parallel connection. When connected in this manner the voltage of the battery is the same as that of a single cell, but the current is equal to the amperage of a single cell multiplied by the number of cells. Thus with 1-1/2 volt 15 ampere dry cells, the combination or battery connected as shown would give 4 × 15 = 60 amperes at a pressure of 1-1/2 volts.] [Illustration: FIG. 74.--Diagram of a series multiple connection. Two sets of cells are connected in series and the two batteries thus formed, connected in parallel. The pressure equals the voltage of one cell, multiplied by the number of cells in one battery, and the amperage, that of one cell multiplied by the number of batteries. This form of connection is objectionable unless all the cells be of equal strength. If old cells be placed on one side and new cells on the other, current will flow (as in fig. 75) from the stronger through the weaker until the pressure of all the cells thus becomes equal. This process therefore wastes some of the energy of the strong cells.] _A paralleled or multiple connection adds the amperage of each cell; that is, the amperage of the battery will equal the sum of the amperage of each cell._ For instance, four cells of twenty-five amperes each would give a total of one hundred amperes when connected in parallel. A series multiple connection, fig. 74, consists of two series sets of cells connected in parallel. In series multiple connections the voltage of each set of cells or battery must be equal, or the batteries will be weakened, hence each battery of a series multiple connection should contain the same number of cells. _The voltage of a series multiple connection is equal to the voltage of one cell multiplied by the number of cells in one battery, and the amperage is equal to the amperage of one cell multiplied by the number of batteries._ [Illustration: FIG. 75.--Diagram to illustrate incorrect wiring. The current pressure of the six cell battery being greater than that of the smaller unit, current will flow from the former through the latter until the pressure of the six cells is equal to that of the four cells.] Fig. 75 shows an incorrect method of wiring in series multiple connection. If the circuit be open, the six cells, on account of having more electromotive force than the four cells, will overpower them and cause a current to flow in the direction indicated by the arrows until the pressure of the six cells has dropped to that of the four. This will use up the energy of the six cells, but will not weaken the four cell battery. This action can be corrected by placing a two-way switch in the circuit at the junction of the two negative terminals so that only one battery can be used at a time. CHAPTER V CONDUCTORS AND INSULATORS