Electric lighting can be obtained by means of arc or incandescent lamps. The arc light is now well understood to be caused by the extremely high temperature of the end of one or both the carbon electrodes. The voltaic arc, Fig. 3, is formed by the minute particles of carbon in a high state of combustion which the current appears to break off and carry from one electrode to the other, the light, however, being mainly due to the incandescence of the crater shown in Fig. 3 on the upper carbon. In the incandescent or glow lamp light is produced by the passage of a current of electricity through a continuous fine thread or filament of carbon which becomes white-hot, the destruction of the filament being prevented through its enclosure in a glass bulb from which the air is exhausted. Figs. 4 and 5. The first method is suitable for the lighting of streets where a high-class illumination is required; also will be wanted for the external lighting of shops, public-houses, and places of amusement, so that arrangements must be made for arc lighting. The usual plan is to charge at the same rate per Unit by meter as the incandescent lamps, but to make an additional charge of 5_s._ to 7_s._ 6_d._ per lamp per quarter for rent, and a further charge of 3_s._ per week for cleaning and trimming. The principal types are the Edison and the Swan, Fig. 4 and Fig. 5. Incandescent lamps can be obtained to order from 1½ candle-power upwards, but the 16 candle-power (nominal 20) or the 8 candle-power (nominal 10) lamps are almost invariably employed. The latter give the best effect, and can be worked to 10 candle-power without much risk, they take about 30 watts as against 60 watts for the 16 candles; and are not uneconomical, for nearly double the number can be worked with the same energy. A new type of glow lamp, called the “Sunbeam,” has been recently introduced, which contains a thick filament, and gives a light of from 200 to 1500 candle-power, and can be employed instead of an arc lamp with the same economy as the ordinary 16 candle-power type. [Illustration: FIG. 4. FIG. 5.] _Life of Incandescent Lamps._