Up until the 17th century, lighthouses were illuminated with beacon fires fueled with wood or coal. The drawback was that the smoke would dull the lantern glass and limit the projection of the light. Lighthouse lighting devices, evolved more or less at the same pace as their domestic counterparts. Oil lamps, gas-mantle lamps and petroleum lanterns succeeded one another as the new illuminants of choice. But it was at the end of 19th century that lighthouses lighting attained adequate intensity and range, thanks in large part to the advent of the electric lamp and improvements made to the compound lens. The latter, design in 1822 by French physicist Augustin Fresnel. Consists of several rings of lenses arranged to refract the light into a narrow, horizontal beam. The Fresnel method still forms the basis of most lighthouse optical systems in use today. Other development, includes system of identifying lighthouses by the pattern of intervals of light and darkness, and a distinctive lighthouse wound signal now alters mariners when there is fog.
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