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Rh Candle Power of Incandescent and Arc Lamps,” ''Phil. Mag.'' (1905); the Preliminary Report of the Sub-Committee of the American Institute of Electrical Engineers on “Standards of Light”; Clifford C. Paterson, “Investigations on Light Standards and the Present Condition of the High Voltage Glow Lamp,” ''Jour. Inst. Elec. Eng.'' (January 24, 1907); J. Swinburne, “New Incandescent Lamps,” ''Jour. Inst. Elec. Eng.'' (1907); L. Andrews, “Long Flame Arc Lamps,” Jour. Inst. Elec. Eng. (1906); W. von Bolton and O. Feuerlein, “The Tantalum Lamp,” The Electrician (Jan. 27, 1905). Also the current issues of The Illuminating Engineer.

Commercial Aspects.—The cost of supplying electricity depends more upon the rate of supply than upon the quantity supplied; or, as John Hopkinson put it, “the cost of supplying electricity for 1000 lamps for ten hours is very much

less than ten times the cost of supplying the same number of lamps for one hour.” Efforts have therefore been made to devise a system of charge which shall in each case bear some relation to the cost of the service. Consumers vary largely both in respect to the quantity and to the period of their demands, but the cost of supplying any one of them with a given amount of electricity is chiefly governed by the amount of his maximum demand at any one time. The reason for this is that it is not generally found expedient to store electricity in large quantities. Electricity supply works generate the electricity for the most part at the moment it is used by the consumer. Electric lamps are normally in use on an average for only about four hours per day, and therefore the plant and organization, if employed for a lighting load only, are idle and unremunerative for about 20 hours out of the 24. It is necessary to have in readiness machinery capable of supplying the maximum possible requirements of all the consumers at any hour, and this accounts for a very large proportion of the total cost. The cost of raw material, viz. coal, water and stores consumed in the generation of electricity sold, forms relatively only a small part of the total cost, the major part of which is made up of the fixed charges attributable to the time during which the works are unproductive. This makes it very desirable to secure demands possessing high “load” and “diversity” factors. The correct way to charge for electricity is to give liberal rebates to those consumers who make prolonged and regular use of the plant, that is to say, the lower the “peak” demand and the more continuous the consumption, the better should be the discount. The consumer must be discouraged from making sudden large demands on the plant, and must be encouraged, while not reducing his total consumption, to spread his use of the plant over a large number of hours during the year. Mr Arthur Wright has devised a tariff which gives effect to this principle. The system necessitates the use of a special indicator—not to measure the quantity of electricity consumed, which is done by the ordinary meter—but to show the maximum amount of current taken by the consumer at any one time during the period for which he is to be charged. In effect it shows the proportion of plant which has had to be kept on hand for his use. If the indicator shows that say twenty lamps is the greatest number which the consumer has turned on simultaneously, then he gets a large discount on all the current which his ordinary meter shows that he has taken beyond the equivalent of one hour’s daily use of those twenty lamps. Generally the rate charged under this system is 7d. per unit for the equivalent of one hour’s daily use of the maximum demand and 1d. per unit for all surplus. It is on this principle that it pays to supply current for tramway and other purposes at a price which primâ facie is below the cost of production; it is only apparently so in comparison with the cost of producing electricity for lighting purposes. In the case of tramways the electricity is required for 15 or 16 hours per day. Electricity for a single lamp would cost on the basis of this “maximum-demand-indicator” system for 15 hours per day only 1.86d. per unit. In some cases a system of further discounts to very large consumers is combined with the Wright system. Some undertakers have abandoned the Wright system in favour of average flat rates, but this does not imply any failure of the Wright system; on the contrary, the system, having served to establish the most economical consumption of electricity, has demonstrated the average rate at which the undertakers are able to give the supply at a fair profit, and the proportion of possible new customers being small the undertakers find it a simplification to dispense with the maximum demand indicator. But in some cases a mistake has been made by offering the unprofitable early-closing consumers the option of obtaining electricity at a flat rate much lower than their load-factor would warrant and below cost price. The effect of this is to nullify the Wright system of charging, for a consumer will not elect to pay for his electricity on the Wright system if he can obtain a lower rate by means of a flat rate system. Thus the long-hour profitable consumer is made to pay a much higher price than he need be charged, in order that the unprofitable short-hour consumer may be retained and be made actually still more unprofitable. It is not improbable that ultimately the supply will be charged for on the basis of a rate determined by the size and character of the consumer’s premises, or the number and dimensions of the electrical points, much in the same way as water is charged for by a water rate determined by the rent of the consumer’s house and the number of water taps.

Most new houses within an electricity supply area are wired for electricity during construction, but in several towns means have to be taken to encourage small shopkeepers and tenants of small houses to use electricity by removing

the obstacle of the first outlay on wiring. The cost of wiring may be taken at 15s. to £2 per lamp installed including all necessary wire, switches, fuses, lamps, holders, casing, but not electroliers or shades. Many undertakers carry out wiring on the easy payment or hire-purchase system. Parliament has sanctioned the adoption of these systems by some local authorities and even authorized them to do the work by direct employment of labour. The usual arrangement is to make an additional charge of d. per unit on all current used, with a minimum payment of 1s. per 8 c.p. lamp, consumers having the option of purchasing the installation at any time on specified conditions. The consumer has to enter into an agreement, and if he is only a tenant the landlord has to sign a memorandum to the effect that the wiring and fittings belong to the supply undertakers. Several undertakers have adopted a system of maintenance and renewal of lamps, and at least one local authority undertakes to supply consumers with lamps free of charge.

There is still considerable scope for increasing the business of electricity supply by judicious advertising and other methods. Comparisons of the kilowatt hour consumption per capita in various towns show that where an energetic

policy has been pursued the profits have improved by reason of additional output combined with increased load factor. The average number of equivalent 8 c.p. lamps connected per capita in the average of English towns is about 1.2. The average number of units consumed per capita per annum is about 23, and the average income per capita per annum is about 5s. In a number of American cities 20s. per capita per annum is obtained. In the United States a co-operative electrical development association canvasses both the general public and the electricity supply undertakers. Funds are provided by the manufacturing companies acting in concert with the supply authorities and contractors, and the spirit underlying the work is to advertise the merits of electricity—not any particular company or interest. Their efforts are directed to securing new consumers and stimulating the increased and more varied use of electricity among actual consumers.

All supply undertakers are anxious to develop the consumption of electricity for power purposes even more than for lighting, but the first cost of installing electric motors is a deterrent to the adoption of electricity in small factories and shops, and most undertakers are therefore prepared to let out motors, &c., on hire or purchase on varying terms according to circumstances.

A board of trade unit will supply one 8 c.p. carbon lamp of 30 hours or 30 such lamps for one hour. In average use an incandescent lamp will last about 800 hours, which is equal to about 12 months normal use; a good lamp will frequently last more than double this time before it breaks down.