An ordinary storage battery used in automobile ignition and lighting systems is of the 6-volt, 60-ampere type, called in trade a "6-60." Lamps can be had for these batteries ranging in sizes from 2 candlepower to 25 candlepower. A lamp of 15 candlepower, drawing 2-1/2 amperes, is used for automobile headlights, and, as any one knows after an experience of meeting a headlight on a dark road, they give a great deal of light. A "6-60" battery keeps one of these lamps running for 24 hours, or two lamps running 12 hours. A minimum of wiring would be required to install such a battery for the reading lights in the sitting room, and for a hanging light in the dining room. The customary gates for charging these batteries in a large city is 10 cents; but in a country plant it could be made less. To charge such a battery on a 110-volt direct current, it is necessary to install some means of limiting the amount of current, or in other words, the charging rate. This charging rate, for 8 hours should be, as we have seen, one-eighth of the ampere-hour capacity of the battery. Thus a "6-60" battery would require a 7-1/2 ampere current. Connecting two such batteries in "series" (that is, the negative pole of one battery to the positive pole of the second) would make a 12-volt battery. Ten or twelve such batteries could be connected in "series," and a 110-volt direct current generator would charge them in 8 hours at a 7-1/2 ampere rate. The diagram on page 259 shows the connections for charging on a 110-volt circuit. An ordinary 16-candlepower carbon lamp is of 220 ohms resistance, and (by Ohm's Law, C equals E divided by R) permits 1/2 ampere of current to flow. By connecting 15 such lamps across the mains, in parallel, the required 7-1/2 amperes of current would be flowing from the generator through the lamps, and back again. Connect the battery in "series" at any point on either of the two mains, between the lamps and the generator, being careful to connect the positive end to the positive pole of the battery, and _vice versa_. Lamps are the cheapest form of resistance; but in case they are not available, any other form of resistance can be used. Iron wire wound in spirals can be used, or any of the many makes of special resistance wire on the market. First it is necessary to determine the amount of resistance required. We have just seen that the charging rate of a 60-ampere hour battery is 7-1/2 amperes. Applying Ohm's Law here, we find that ohms resistance equals volts divided by amperes, or R = 110/7.5 = 14.67 ohms. With a 220-volt current, the ohms resistance required in series with the storage battery of this size would be 29.33 ohms. _Automobile Power for Lighting_