COAL FIRES IN LIGHTHOUSES

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doubt, would sometimes be the case; at other times, doubtless, it would not be seen from five miles off. These coal fires, even if they had been a good means of illumination, which they were not, were, of course, never applicable to an isolated rock lighthouse; no lighthouse of that description being able to afford storage room for the quantity of coal that would be required; to say nothing of the difficulty that would very frequently be experienced by vessels in getting alongside with the requisite supplies. Coal fires, however, were retained at many shore lighthouses until well into this century, the Isle of May Lighthouse, at the entrance of the Firth of Forth, having a coal fire until 1810; the lighthouse at Flat Holm, in the Bristol Channel, having also a coal fire until 1820; and that on St. Bee's Head, Cumberland, until 1823; whilst at certain lighthouses abroad the coal fire was still in use down to 1850.

Wherever it is equally efficacious, a shore lighthouse is always very much to be preferred to an isolated rock lighthouse, not only on account of its being in every way much more accessible, but as the opportunity then exists for the erection of all the numerous subsidiary buildings that are required at a first-class lighthouse; the engine-house in connection with the electric light, the house for the fog-syren, and very much better quarters for the men. As a typical example of such a shore lighthouse, with all its accessory buildings, we give an illustration of the Lighthouse at St. Catherine's Point, at the back of the Isle of Wight. This lighthouse, when viewed from seaward, is seen against a background formed of grass, and trees, and all the verdure of the Undercliff, and is therefore, with all its outbuildings, painted a most dazzling white.

CHAPTER XXVI.

The means of illumination-The catoptric and the dioptric systems—The catoptric system-Primitive reflectors-More recent improvementsFixed lights-Revolving lights-M. Augustine Frenel-The dioptric system-The French lights-Mr. Stevenson's improvements-The apparatus The lenses-The lamp-Evidence as to the dioptric system given before the Royal Commission-Distances at which lights are visible -Experiments at the South Foreland-Electric lights-Mineral oilGas-Report of the Committee-Control of lights-The Trinity HouseOther bodies-Lightships-Their lights-Revolving lights-Flashing lights-The moorings of lightships-Casualties to lightships-Crew of a lightship-Relative visibility of lights-Gongs and sirens-Beacons-Buoys-Bell buoys-Whistling buoys-Gas buoys-Communication between lightships and the shore-Light dues-The different rates-The present mode of collection-Thorough reform needed.

THERE are two distinct systems employed for the illumination of lighthouses and lightships, one of which is known as the catoptric, or the reflector system, the other as the dioptric, or the lens system. Every ordinary uncontrolled light gives off its rays in every direction, forming a globe, in fact, of which the wick is the centre, the rays of light being horizontal, and from horizontal at all angles, both upwards and downwards, to vertical. Now, for lighthouse purposes it is obvious that all the vertical rays, whether tending upward or downward, are entirely lost and wasted, and it was early seen that to obtain the full effect of a light, and to utilize these vertical rays they must be bent into a horizontal direction. To effect this purpose reflectors were adopted, and the earliest improvement upon the then existing system of lighthouse illumination was the adoption of the catoptric or the reflector system, and the earliest type of reflector was that applied to the Cordouan light in 1727.