On a further comparison of results, it was found that the light of one of the great annular lenses, used in the revolving lights of the first order, was equal to the united effect of about eight of the large reflectors employed in the revolving lights on the Scottish coast. At the Isle of May and Inchkeith the quantity of sperm-oil consumed by the great lamp is equal to that burned by fourteen of the Argand lamps used in the Scotch lights. Hence by dioptric means the consumption of oil necessary for the fourteen reflectors will produce almost as powerful a light as that which would require the oil of twenty-four reflectors in the catoptric system, and consequently there is an excess of oil equal to that consumed by ten reflectors, or four hundred gallons in the year against the Scotch system. The Dutch were the first to adopt Fresnel’s system. In the year 1834 the Commissioners of Northern Lighthouses sent Mr. Alan Stevenson to Paris to inspect the system, and his report was so favourable, that the reflecting apparatus of the revolving light at Inchkeith was removed, and the dioptric instruments substituted. The new light was exhibited on the evening of the 1st of October, 1835, and so great was the satisfaction afforded, that a similar change was made at the fixed light of the Isle of May. The Trinity-House of London followed next in adopting the improved system, and a revolving dioptric light of the first order was erected at the Star Point in Devonshire. In the lighthouses of this country sperm-oil is the most usual fuel. In France[6] an oil is burned called Colza oil, expressed from the seeds of a species of wild cabbage. In the lighthouses on the Mediterranean olive-oil is used. In a few lighthouses near large towns coal-gas has been advantageously adopted. Much also has been said in favour of the Drummond and Voltaic lights, which, on account of their prodigious intensity would appear to be most desirable; but the uncertainty which attends their exhibition renders it at present impossible to adopt them: but there is a yet more fatal objection--the smallness of the flame renders them wholly inapplicable to dioptric instruments, which require a great body of flame in order to produce a degree of divergency sufficient to render the duration of the flash in revolving lights long enough to answer the purpose of the mariner. In the year 1835, Mr. Gurney proposed a lamp of great power in which the flame of oil or wax was sustained by streams of oxygen gas, a method said to be more economical than the combustion of oil in atmospheric air. The Trinity House entertained the proposal, and instituted a number of experiments. In applying this light to reflectors it is intended to use three small flames, each about three-eighths of an inch in diameter, productive, it is said, of an effect equal to that of ten Argand lamps. But for lenses the burner has seventeen films of flame, and is said to possess six times the power of the Fresnel lamp.