The power of the arc-light is something unrivalled by any other light, whether of limelight or magnesium. At the famous Crystal Palace Electrical Exhibition, an arc reputed to be one hundred and fifty thousand candles in power was lighted every evening. The carbons were stout copper-plated bars nearly two and a half inches thick. This intensity of illumination renders the arc eminently adapted for lighthouses and search-lights. Hence it is that the French government have decided to light forty of their coast lighthouses by electricity, and that most of our warships and military trains are now equipped with electric lamps for searching purposes. We read that the fleet at Alexandria explored the Egyptian forts by night with powerful arcs; and that the French Admiral at Madagascar struck terror into the breasts of the simple Hovas by a similar display. For scouring the sea in search of torpedo-boats by night, or icebergs and other ships during a fog, the value of the arc-light cannot be too highly estimated. The screw-steamer _Faraday_, while engaged some time ago in laying a new Atlantic cable, would have run right into an iceberg in a Newfoundland fog, but for the electric beam projected from her bows into the misty air ahead. Fog, however, has a peculiarly strong quenching power over the arc-light, owing to the preference it has for absorbing all the blue rays, and to the comparative poverty of the orange colour. Hence it is that electric arc-lamps look so white and dim in a dense fog. A single gas-jet can be seen about as far as a two-thousand-candle arc-lamp. This is because the gas-jet is rich in those red rays which penetrate a fog without being absorbed; whereas it is poor in the blue rays which are quenched. For this reason, also, the incandescence lamp is preferable to the arc for a misty atmosphere. The incandescence lamp can also burn under water, and owing to its pretty shape, its pure light, its cleanliness, and independence of everything except wires to bring the current to it, is highly suitable for decorative purposes. It particularly lends itself to ornamental devices of a floral order; and a great variety of chandeliers and brackets have now been designed representing various plants with leaves of brass or filagree, and flowers composed of tinted crystal cups containing the lamps. Fruit is also simulated by lamps of coloured glass. For example, at a Drury Lane Christmas pantomime, both holly and mistletoe berries were imitated by incandescence lamps of crimson and opal glass. Artificial lemon-trees, with fruit consisting of yellow lamps, also make a pretty dining-table ornament. So do vases of roses with incandescence lamps hid in them, an ornament devised by Mr J. W. Swan for his residence at Bromley. Aquaria, too, can be lighted internally by incandescence bulbs, and it would be very pretty to see the lamps lying beside growing sea-anemones, whose expansion might seem the more lovely under the stimulus of their rays.