536 SEC. 12. APPLIED MECHANICS. 



weather, and in thick weather the three inner wicks (at other times cut off by 

 a concentric reflector) are also brought into action. The full light-producing 

 power of the six-wick lamp is equal to 722 standard sperin candles, attained 

 by a consumption of 1 gallon of oil in 1 hour 50 minutes ; its half-power 

 equals 342 candles, with 1 gallon consumed in 2 hours 45 minutes. By a 

 simple arrangement regulating the level of oil in the burner, and the position 

 of the air-deflectors, the lamp can be made to bum any description of oil at 

 pleasure. 



2189. Panel of Cata-Dioptric Apparatus, One of a set 

 of Polyzonal Lenses manufactured in 1836 by Messrs. Cookson 

 and Sons, of Newcastle, for the Trinity House of London, and 

 by them fixed in the Start Point Lighthouse, Devonshire. 



Trinity House, London. 



The first lenticular apparatus used in an English lighthouse, with a central 

 lamp upon Fresnel's principle. 



2190. PlanoConvex Lens, used at Portland Lighthouse 

 in the year 1789. Trinity House, London, 



It is 22 inches in diameter, and was placed in front of an argand burner 

 and reflector. It is believed to be one of the lenses first used in combination 

 with an oil lamp and reflector for lighthouse illumination. 



2191. Pacet Heiiector. Specimen of a reflector and lamp 

 used first at Liverpool about the year 1763, and afterwards at 

 Lowestoft and other lighthouses. Trinity House, London. 



It is made of wood with facets of silvered glass, is nearly paraboloids! in 

 form, and is the earliest kind of reflector known to have been used in aid of 

 an oil lamp in lighthouse service. 



2192. Lamp and Reflector, as used in English floating lights 

 about the year 1809. The curve of the reflector is spherical. 



Trinity House, London. 



2193. Bhu Heartach Lighthouse, situated on a rock on 

 the West Coast of Scotland, exposed to the force of the Atlantic 

 Ocean, and 14 miles from lona, the nearest land. Designed and 

 executed by D. & T. Stevenson, Engineers to the Board. Com- 

 menced 1867, finished 1872. 



The Commissioners of Northern Lighthouses. 



2195. Model of a First-class fixed Dioptric Light; 



scale, one-fifth of full size. 



The Commissioners of Northern LightJtouses. 



This apparatus consists of a central lenticular band, and an upper and 

 lower set of reflecting prisms. The cylindrical belt with diagonal joints and 

 the upper and lower reflecting prisms were substituted by Mr. Alan Steven- 

 son, in 1836, for the segmental belt, and upper and lower silvered mirrors of 

 Fresnel's first-class apparatus. 



