For example: 16 candle-power Swan lamps are assumed to take 60 Watts, which, if the electrical pressure is 100 Volts, would mean a consumption of 0·6 Ampère; and, as an Electrical Horse-power equals 746 Watts, 12·4 lamps should theoretically be obtained per Horse-power, which is, however, reduced in actual practice to 10 at the most, often less. The charge per Unit supplied by meter varies in England from 1_s._ to 7_d._ Price for electric Equivalent price for gas of equal light. light. _s._ _d._ _s._ _d._ 1 0 } per Board { 6 10 per 1000 cubic feet. 0 9 } of { 5 1½ ” ” 0 7¼ } Trade { 4 2 ” ” 0 6 } Unit. { 3 5 ” ” _Comparison of Cost of Gas and Electricity._ These prices, of course, include the manufacturer’s profit as well as the loss in transmission through the mains and expenses of connecting up to the consumer. The actual manufacturing cost of a station maintaining 10,000 lights should not be more than 3_d._ per Unit, or equivalent to gas at 1_s._ 8½_d._ per 1000 cubic feet.[2] [2] See Table IV., page 87. As petroleum lamps are used for the street lighting of many foreign and colonial towns, the question arises, “Will it pay to substitute the electric light?” Comparing the light given by a kerosene or petroleum lamp with that from the incandescent electric lamp, the cost is greatly in favour of oil; and, in fact, where the price of kerosene is under 1_s._ per gallon, electricity cannot compete if labour is cheap. On the other hand, the trimming, lighting, and keeping in order of a number of lamps scattered over a large area greatly augments the working cost, to which must be added the breakages of chimneys, expense of wicks, also the danger of fire. It is the safety of electricity which has caused it to supplant oil both for public and private lighting in American cities; even where the price of kerosene is not more than 6_d._ per gallon there is a demand for the electric light, which is by far the dearer illuminant, after making a liberal allowance for labour in cleaning, filling, and lighting the oil lamp, also for depreciation of the burners. _Arc and Incandescent or Glow Lighting._ [Illustration: FIG. 3.]