in a vessel’s signal lights, especially her side lights, whereby an increased luminous range can be secured and the risk of collision greatly lessened. The vertical angle subtended by lenticular refracting apparatus has been increased from 45° and 47° to 80°, and even by the use of dense flint glass to 92°. In this way the normal power of the central or lens portion of a light, always two-thirds of the whole power, has been so augmented that it is found advisable to dispense with the prisms both upper and lower, and to depend on the refractors alone. When higher degrees of intensity are needed, a second tier of lenses can be superposed on the first, and a third and fourth added, a separate flame being in the focus of each tier. This has been done by Mr. Wigham, of Dublin, with gas flames, and by Sir James Douglas with oil flames. The two great divisions of lighthouse apparatus into fixed sections and revolving sections have been extended. Thus the old fixed light, the revolving light with equally recurring single flashes, the composite fixed and flashing light, always objectionable from its unequal power, have been supplemented by the occulting light, and the group flashing light which last was designed by Dr. John Hopkinson, and first constructed by Messrs. Chance. In this arrangement the beams are sent out in groups, each beam of the group being separated from one another by a short interval of time, and each group by a longer interval. The lights on a coast can thus be distinguished by their single flash, double flash, or triple flash.[56] ILLUMINANTS AND BURNERS.--Mineral oil has been introduced, and special burners designed in order to burn it. The largest of the old colza oil burners (known as Fresnel burners) has an intensity of 230 candle units, or 23·6 candle units per square inch, while a similar burner for paraffin has been reported as affording 415 candle units, or 44·3 units. The latest developed Trimley burner of Sir James Douglas, with nine concentric wicks, gives 49·8 units. The oil used has a flashing point of 154° F. The average cost of mineral oil is one-fourth that of vegetable oil. Gas is also freely employed, and in the 108-jet burner of Mr. Wigham it has attained a power of 2,433 candles, and in the 10-ring burner of Sir James Douglas, a power of 2,619 candles. Beyond the highest reach of oil or gas burners, say 2,500 or 2,600 candles, is the electric arc giving an intensity of beam of ten millions of candles. At the other end of the scale is the duplex burner, which, with the new Chance lenses, is available in the smallest apparatus for a horizon of from seven to ten miles.