:SOURCES OF LIGHT. The deseriptions which have already been given have all had reference to the best means of employing a !riven light. Many attempts have from time to time been made to increase the power of the radiant it-elf. The illuminant of the lighthouse establishment has been changed frequently. The earliest one used on the North American (-oast consisted of balls of pitch and oakum burned in open braziers at Point Allerton, in 1673. which was succeeded by tallow candles at Bo-ton Harbor in 1116. Next came fish nil, burned in spider lamps, and afterwards sperm oil. burned in a sort of argand lamp in Win-low's magnifying and reflecting lanterns, which remained in use up to the time of the establishment of the Lighthouse Board. As sperm c.il became more and more ex pensive, the attention of the hoard was directed to finding cheaper illuminant, and it was found that colza, the oil expressed from the seeds of wild cabbage and several other plants. which was largely used in France and (treat Britain, would fulfill all the conditions except that of being of home production. This was overcome by stimulating the cultivation of the plants and the manufacture of the oil from the seeds as a private industry. Further experiments with lard oil were made, with such success as to prove that the latter oil of a certain grade was at more desirable illuminant than colza, as it was more certain in quantity and production and was more economical in price. This be came the next established illuminant. The use of petroleum had attracted attention for a long time, and in 1855 the Light house Board made some unsuccessful experiments with it. Meantime the price of lard oil had so increased that some other illuminant became a necessity, and as mineral oil in one form or an other was in successful use in European light houses, the board renewed it. experiments with petroleum. The first difficulty was that of the lamp in which it should he burned. This was finally overcome by the board. succeeded in producing a lamp in its own laboratory that proved satisfactory and that was introduced into the lighthouses. The following qualities
were determined by the board in reference to petroleum: It fixed the flashing test of the mineral oil that would be accepted for light house use at 140' F., the fire-test at and the freezing test. at which it would remain limpi at zero. Litmus paper in it for five hours must. by remaining unchanged in odor, show its freedom from acid : it- -pecifie gra\ ity must not he less than and it is to be paid for by weight, at the rate of 6 '410 net weight to the gallon. The difficulty of st, ring and transperting such quantities in bulk was conceded, but its danger was evaded by having the nil placed at once in five-gallon cans, where it was to remain until transferred to the light house burners for combustion. Mineral oil is now used throughout the lighthouse establish ment. It is claimed that live gallons of mineral oil will give as much light as four gallons of lard oil, while mineral oil at the present writing costs about SI_ cents, and lard oil 57 cents per gallon. The highest. price paid for mineral oil since the board commenced to use it in large quantities was 30 vents per gallon; the lowest cents. A certain class of lights are shown at the ends of long piers, which are often dan gerous to reach in heavy weather, when they are swept by the waves and wind. For this pur pose a burner has been invented on the constant level principle, which will keep a light burning for six and even eight days and nights without attention, so the light need only be visited in safe weather.
GAS. The use of gas has been attempted in a number of places. Accidents to the gas-pipes are most liable to occur in very bad weather, when repairs are most difficult to make. Com pressed gas supplied from tanks is in use for lighting buoys (q.v.) and inaccessible beacons. A combination gas-machine is used to furnish the light to some of the stations on the North weste•n lakes. This machine works automati cally, making the gas from gasolene and fur nishing a light which can burn, according to the size of the machine, from thirty to ninety days without attention.