Rodney Barfield, in his book Seasoned by Salt, explains: "The Fresnel (pronounced Fre-NEL) lens developed by French physicist Augustin Fresnel, was a technological leap in navigational lighting. It is a glass dome of prisms and bull's-eyes, and light is concentrated at its center into parallel rays that are intensified with a magnifying glass."
This is a photo of the fourth order Fresnel lens in the Ocracoke lighthouse. Although the Fresnel lens was invented in 1822, and the Ocracoke lighthouse was built in 1823, a Fresnel lens was not installed until 1854.
The Ocracoke light (now produced by a 250 watt quartz-halogen bulb, and magnified by the lens) is equal to 8,000 candlepower, and is visible 14 miles to sea.
Our latest Ocracoke Newsletter is the story of late 19th century steamship traffic to Ocracoke, and the large Victorian hotel that accommodated the guests. You can read the article here: http://www.villagecraftsmen.com/news082114.htm.