tions. Its development may be greatly accelerated when costs are decreasing, and a wise business policy will urge the advantages of improved lighting where favorable prices occur.

GOOD PUBLIC POLICY

A careful far-seeing public policy, after providing for good service with all that that requires, will proceed to the education of the public in the possibilities of the illumination of the city and the ability of the contractor to furnish such illumination at reasonable rates.

This function naturally devolves on the public utility. With this in view, it is not enough to restrict one's efforts to the requirements of the day. The relations between the city and company should be such as to make it possible for the company to show the city the improvements in the art as they occur, and to explain how the city can best use its available funds in the increase and improvement of the street lighting so as to attract people and business to it. This effort should be continuous and of the same general persistence used for commercial customers, and the utility should remember that it has a dual responsibility in the improvement and welfare of the city, for what helps the city helps the company.

Even if this were done without profit or with a relatively low rate ́of return, the effort would be justified from the increased business derived from the general improvement. It is difficult to imagine a better method for the advancement of street illumination or for retaining the good will of a community.

RAILWAY CAR LIGHTING

BY GEORGE H. HULSE

The proper lighting of railway cars has always offered special problems, both in regard to the methods employed in producing the energy for lighting, and in the application of the light sources to obtain proper illumination.

As methods of lighting have been improved, the new methods have been applied to the lighting of cars with such modifications as the special conditions make necessary. Oil lighting superseded candles, gas displaced oil lighting, and for a time completely dominated the field, but at the present time, as in other places, the field is divided between gas and electricity.

GAS LIGHTING

Practically all cars using gas light employ oil gas as the illuminant. As the storage space available is limited, it is necessary to carry the gas under pressure in order to have a sufficient supply on the car, and also to have a gas of comparatively high illuminating value. Coal gas, of low candle-power primarily, loses at least 50 per cent. of its illuminating value when compressed to a point high enough to give sufficient storage. Oil gas has not only a much higher candlepower uncompressed, but when compressed to ten atmospheres, loses only 10 per cent. of its illuminating power.

Oil gas is made by the distillation, or "cracking" of petroleum oil in cast iron or clay retorts, or in steel generators filled with fire brick checker work. A fixed gas is formed which has for its principal ingredients methane and heavy illuminants with a very small amount of hydrogen. It has a heating value when compressed of 1250 heat units per cubic foot. After passing through proper washing and purifying apparatus, the gas is compressed to 12 atmospheres in store holders, from which it is carried to the railroad yards by suitable pipe lines. The car holders are filled from these pipe lines. The car equipment (see Fig. 1) consists of one or more welded steel holders to contain the gas supply, two filling valves, a pressure gauge, a regulator for reducing the holder pressure to that at

which the lamps operate, the pipe line for carrying the gas from the holders to the lamps, and the lamps or burners. All fittings for both the low-pressure and high-pressure piping are especially designed for the work. The pressure regulator is placed under the car near the holders so that the amount of high-pressure piping is small and none of it is inside the car.

The pressure regulator reduces to the proper pressure and maintains this pressure constant with the varying amounts of gas used. At the beginning oil gas was burned in regenerative lamps with a cluster of from two to four burners of the union jet type. All lamps used at the present time are fitted with incandescent mantles.

One of the early, and probably the earliest completely successful application of the inverted mantle was to car lighting. This was

due to the fact that while the development of the inverted mantle for general use had to contend with low and varying pressure, in car lighting a sufficient and uniform pressure was at all times available.

In this country two sizes of mantle are used, one which gives 28 candle-power, with a gas consumption of o.8 cubic feet per hour, the gas pressure being 1 pound per square inch. The use of this size mantle is limited to bracket lamps, and a few installations in which four of these mantles are employed in a cluster for center lighting.

The other size of mantle, which is used for center lamps giver 90 candle-power, with a gas consumption of 2 cubic feet per at 2 pounds pressure per square inch.

The mantles used are of a special form and compositio

stand the rigors of railway service, and give three months average life in service.

There are upward of 85 gas plants for the manufacture of oil gas in the United States and Canada. Gas is delivered to the car holders and charged for at a uniform rate, the amount of gas supplied being measured by the increase of gauge pressure.

The holders are made exact size and the contents of a holder can always be determined by multiplying its capacity by the gauge pressure in atmospheres. This feature, besides furnishing a means of measuring the amount of gas supplied, is important for determining the hours of lighting which a holder contains and also for the purpose of car interchange.

Cars using oil gas are dependent upon stationary plants, but this has not been found to be a disadvantage, principally because the time required to charge a car is so short. It can be done, if necessary, at a division station stop.

ELECTRIC LIGHTING

Three methods of electric lighting for railway cars are in use:

1. The head-end system.

2. Straight storage.

3. Axle-driven generators.

The Head-end System.-In the head-end system use is made of a generator driven by a steam engine at the head of the train, either in the baggage car or on the locomotive. Electrical energy is carried back from the generator to the cars to be lighted by means of a train line on the car roof and connectors between the cars.

In this country the generator of a head-end system is usually installed in the baggage car, and is driven by a steam turbine, steam for its operation being brought from the locomotive through suitable hose connections. A very few equipments are in service with the generating set mounted on the locomotive, but this entails heavy installation cost, since several locomotives may be used in hauling one train over its trip.

As the steam supply is shut off when the locomotive is detached from the train it is necessary to have a storage battery on one of more of the cars to supply light during such time as the locomotive is detached at terminals or division points.

The head-end system gives efficient and economical results, but

its great disadvantage is that light can only be used when a car is in a train with a generator equipment. If the cars are equipped with batteries to supply light during such times as the locomotive is disconnected, the proper arrangements for charging the batteries entail a sacrifice of simplicity and economy.

Straight Storage. In the straight storage system each car is equipped with a set of storage batteries of sufficient capacity to supply energy to the lamps for the desired trip. As ordinarily applied, the equipment is simple, consisting of lamps, storage batteries and charging receptacles, with necessary wiring. At terminal yards the batteries are charged with energy obtained from a stationary power plant. The lamps operate directly from the batteries, no voltage regulator being used.

This system of lighting would be ideal if it were not for the fact that the charging of the batteries consumes too much time. Generally cars are not available in one location long enough to receive proper charge.

The cost of equipping a railroad yard with the proper charging lines is considerable.

Car lighting systems dependent upon stationary plants are feasible as shown by the oil gas system, but the time required for charging must not interfere with car service.

Axle Driven Generators.-In this system the car axle is used to drive a generator which supplies energy for the lamps in the car, and for charging a storage battery which supplies energy to the lamps when the car is running below a certain speed.

The equipment consists of the following:

A generator mounted either on the car body or truck with some form of driving system between the car axle and the generator, a storage battery to maintain the light when the speed of the generator falls below that at which it gives the proper voltage, regulating apparatus to govern the output of the generator at varying speeds, to give the proper charge to the storage battery, and to maintain constant voltage at the lamps, and some means of keeping the polarity of the battery charging current constant when the direction of the movement of the car is reversed.

Various systems have been devised to meet these conditions and a large number are in successful operation on railway cars. The best practice is exemplified by an equipment in which the generator is mounted on the car underframe, the generator controlled for output at varying speeds by a carbon pile rheostat in its field circuit,