If, on the other hand, there is very little resistance in the battery, the current has very little work to flow to the wires leading from the battery, and we can get a larger quantity, or greater number of ampères. Thus, you will see that while the closed-circuit battery is the stronger, and will do all that the open-circuit battery will do, and even more, in a short time the latter, though weaker, will do about as much work for the same amount of zinc and carbon as the former, but takes a much longer time. BATTERIES FOR ELECTRIC LIGHT As we have explained to you, closed-circuit batteries are used for producing incandescent electric lights in small numbers, as well as for running motors. To operate incandescent lights, a number of batteries connected together are used. The number used depends upon the pressure which the lamps require to make them give the required light. We will now explain how the batteries are connected together for this purpose. [Illustration: Fig. 32] Suppose you wished to light an incandescent lamp of, say, three candle-power, which required six volts. We would take three closed-circuit batteries which would each give two volts, and connect by a piece of wire the zinc of the first to the carbon of the second, and the zinc of the second to the carbon of the third, as shown in the sketch. (Fig. 32.) We would then attach a wire to the carbon of the first and one to the zinc of the third, and there would be six volts in these two wires, which would light up one six-volt lamp nicely. This is called connecting in series, or for intensity. Now if each of these cells gave ten ampères alone, the three will only give ten ampères together when they are connected in series. If our lamp only required one ampère, you would naturally think that ten similar lamps put on the wires would give as good light as the one, but that is not so. Although you might light up two lamps, the pressure would drop and the lights would become less brilliant if you put on the whole number. So, if we wished to put on the whole ten lights we would connect another battery and thus increase the pressure, which would probably make these ten lamps burn brightly. These rules hold good for connecting any number of batteries for lamps of any number of volts--that is to say, there should be calculated about two volts for each cell and an allowance made for drop in pressure. CONNECTING IN MULTIPLE There is another way of connecting batteries, and that is to obtain a larger number of ampères. This is called connecting in multiple arc, or for quantity. [Illustration: Fig. 33] Let us take again for an illustration the three cells giving each 2 volts and 10 ampères. This time we connect the carbon of the first to the carbon of the second, and the carbon of the second to that of the third; then we connect the zinc of the first to that of the second, and the zinc of the second to that of the third, as shown in the sketch. (Fig. 33.)