1230
THEORY AND PRACTICE OF ENGINEERING.
Book II.
mercial world is infinitelyindebted for the mass ofevidence there broughtforward on this highly im-portant subject, as the meansof preventing many of thosefatal accidents to which ourshipping is so constantlyexposed.
Till the date of the report,the lighthouses which sur-rounded our coast weremanaged by a variety ofsystems, and, instead of beingunder the superintendenceof the Government, were,many of them, in the handsof private individuals : thewhole appear to have beenbuilt at various times, byslow degrees, and as thenaval and commercial inte-rests required them.
There were belonging to,and under the managementof, the Trinity House ofDeptford Strond in the year1834, 108 lighthouses and 18floating lights, and through-out the United Kingdom 198 lighthouses and 21floating lights. This fra-ternity, or college of seamen, seems to have existed prior to Henry VIII. , but in the sixthyear of that monarch’s reign they were incorporated by charter, as the Master, Wardens,and Assistants of the Guild Fraternity of the Most Glorious and Undivided Trinity, and ofSt. Clement’s, in the Parish of Deptford Strond, in the County of Kent . Queen Elizabethafterwards gave them fresh powers, to erect and preserve beacons and signs for the sea,but it does not appear that this fraternity erected any lighthouses till the year 1676.
The public lights of Scotland were under the Commissioners for Northern Light-houses, incorporated by the 38 George 3 . chap. 58. ; there were 25 lighthouses undertheir management: those of Ireland were under the superintendence of the Ballast Board,a corporation consisting of the mayor and sheriffs of Dublin , three aldermen, and 17other individuals, who had the control and management of 35 lights; there were severalother lighthouses held under lease from the Crown.
Lighting -The first method employed for lighting these buildings was undoubtedly
coal fires, unaided by reflectors or any mechanical or optical arrangements: to this suc-ceeded the use of candles, and till a late period we find them generally adopted : thenext improvement was the Argand burner, introduced on the focus of a parabolicreflector: this instrument is made of silver, strengthened with copper; it is about 3 or4 inches in focal length, and 21 inches in diameter ; the number and arrangement ofreflectors in each house depend on the light being fixed or revolving, as well as uponthe situation and importance of the lighthouse: one of the methods much used in France is to place a large Argand lamp, with four concentric wicks, giving a very powerful light,in the centre of the lantern, surrounding it with a series of glass lenses, of a peculiarconstruction, and using a refracting, instead of a reflecting instrument to collect the light,and only one lamp instead of a number. The lens is a very beautiful instrument, about 30inches square, plano-convex, and formed of separate rings or zones, whose common surfacespreserve nearly the same curvature as if they constituted portions of one complete lens, theinterior and useless part of the glass being removed. To form a lens out of one piece ofglass of such a magnitude would be scarcely practicable, and if it were, the thickness of theglass would materially obstruct the light: a lens so constructed gave as much light as nineof the ordinary reflectors in common use, and the consumption of oil in the burner was asgreat as in seventeen of the Argand lamps.
Lieutenant Thomas Drummond, who was employed on the Trigonometrical Survey ofEngland, had his attention directed to the subject of signal lights, in consequence of thegreat difficulty he experienced in observing distant stations, particularly when it was requiredto see Leith Hill, in Surrey, from Berkhampstead Tower, in Hertfordshire ; and it
Fig. 1929.
PLAN OF RAMSGATE LIGHTUOLSE.