Abroad it is becoming quite common for power companies to deliver storage batteries fully charged, and call for them when discharged.

Without a stretch of the imagination, we can imagine an ingenious farmer possessing a water-power electric plant building up a thriving business among his less fortunate neighbors, with an "electricity"

route. It could be made quite as paying as a milk route.

[Ill.u.s.tration: Connections for charging storage batteries on 110-volt mains]

Many communities have water or steam power at a distance too great to transmit 110-volt current by wire economically; and because of lack of expert supervision, they do not care to risk using current at a pressure of 500 volts or higher, because of its danger to human life.

In such a case it would be quite feasible for families to wire their houses, and carry their batteries to the generating plant two or three times a week to be charged. There are a number of portable batteries on the market suitable for such service, at voltages ranging from 6 to 32 volts. The best results would be obtained by having two batteries, leaving one to be charged while the other was in use; and if the generating station was located at the creamery or feed mill, where the farmer calls regularly, the trouble would be reduced to a minimum.

Such a battery would necessarily be small, and of the sealed type, similar to those used in automobiles. It could be used merely for reading lamps--or it could be used for general lighting, according to the expense the farmer is willing to incur for batteries.

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_

There are many ingenious ways by which an automobile may be utilized to furnish electric light for the home. The simplest is to run wires direct from the storage battery of the self-starting system, to the house or barn, in such a way that the current may be used for reading lamps in the sitting room. By a judicious use of the current in this way, the normal operation of the automobile in the daytime will keep the battery charged for use of the night lamps, and if care is used, such a plan should not affect the life of the battery. Care should be used also, in this regard, not to discharge the battery too low to prevent its utilizing its function of starting the car when it was desired to use the car. However, if the battery were discharged below its starting capacity, by any peradventure, the car could be started by the old-fashioned cranking method.

Using an automobile lighting system for house lighting implies that the car be stored in a garage near the house or barn; as this battery is too low in voltage to permit transmitting the current any distance.

One hundred feet, with liberal sized transmission wires is probably the limit.

That such a system is feasible is amply proved by an occurrence recently reported in the daily papers. A doctor summoned to a remote farm house found that an immediate operation was necessary to save the patient's life. There was no light available, except a small kerosene lamp which was worse than nothing. The surgeon took a headlight off his car, strung a pair of wires through a window, and instantly had at his command a light of the necessary intensity.

Another manner in which an automobile engine may be used for house lighting is to let it serve as the charging power of a separate storage battery. The engine can be belted to the generator, in such a case, by means of the fly wheel. Or a form of friction drive can be devised, by means of which the rear wheels (jacked up off the floor) may supply the necessary motive power. In such a case it would be necessary to make allowance for the differential in the rear axle, so that the power developed by the engine would be delivered to the friction drive.