The maintenance charges are guided by the local market values of materials and labour, the item of repairs and renewals being practically negligible. So far as oil consumption per month is concerned, this fluctuates according to the type of lamp used, ranging from 1-1/5 pints per twenty-four hours, or 4·8 gallons per month, in the case of a 1-1/8-inch single-wick burner, to 2¼ pints per twenty-four hours, or 8¾ gallons of oil per month, in the case of the latest 1-5/8-inch duplex-wick burner. American petroleum-oil, of a specific gravity of about 0·795, gives the best results and the brightest and clearest flame. Russian and other heavier oils generally used in lighthouses are unsuitable. In view of the world-wide operations of the Standard Oil Company, however, no difficulty is experienced in procuring adequate supplies of this oil anywhere between the two Poles. The oil used in the float cylinder, as mentioned previously, is quite distinct from the burning oil, and is used only to support the float to which the wick is attached. As the oil escapes through the drip-valve, it may be allowed to run to waste, or, what is far preferable, it may be caught, filtered, and used again for this purpose, to bring about a reduction in the cost of upkeep. The float cylinder of a thirty-one-day light, irrespective of the number of wicks, requires the same quantity of oil for the float cylinder--9½ gallons. The advantages of the unattended, automatic light have been appreciated by the various maritime Powers, and their application is being developed rapidly. They are inexpensive in first cost, and their maintenance charges are very low. In Sweden a second-order light, consuming 6 cubic feet of acetylene gas per hour, throwing a fixed white light of 4,000 candle-power, and visible for seventeen miles in clear weather, costs about £15, or $75, per annum; while the smaller lights, with a 300-millimetre lens and a 12-inch burner emitting 360 candle-power, may be run for £2, or $10, per annum, the low cost in this instance being attributable to use of the Dalén flasher and sun-valve. The cost of the acetylene gas averages ¾d., or 1½ cents, per cubic foot, a result attributable to the fact that Scandinavia is the world’s largest producer of carbide of calcium.