Beck, Adam. “The Million Dollar Lens: The Science and history behind the Fresnel Lighthouse Lens.” Partsolutions.com.http://partsolutions.com/the-million-dollar-lens-the-science-and-history-behind-the-fresnel-lighthouse-lens/

Fresnel Effect

In the 1700 and 1800’s open water shipping was the lifeline of commerce – it was the only way to transport goods between the continents, but it wasn’t easy. Among the many difficulties was the problem of ships, and all of their precious cargo running aground and being smashed on unseen rocks.

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Through the years seven classifications of Fresnel lenses were developed. These classifications, know as “orders,” were developed to meet all the needs of the many different lighthouses and the diverse coastal environment each lighthouse stood within.

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The smaller Fresnel lens orders, the fourth through sixth orders, were often situated on lakes and harbors because of their limited nature of lens signal and visibility.

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Preston, Dickson J. Oxford: The First Three Centuries. (Easton, MD: The Historical Society of Talbot County, 1984), 202-203

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In the bitter winter of 1918, he faced a similar challenge at Benoni’s Point. A huge ice jam knocked the lighthouse loose from its foundation and it toppled over. On orders from Washington, Faulkner abandoned it. When the ice cleared another lighthouse, said to been virtually identical with the Hooper’s Straight lighthouse now at the Chesapeake Bay Maritime Museum in St. Michaels, was towed up from Cape Charles and installed on the new foundation. This one lasted until it was dismantled by the Coast Guard in 1964, and replaced by an unmanned automatic bell buoy and flasher.

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Captain John E. Faulkner, the Benoni’s Point lighthouse keeper until his death in 1929 at the age of seventy-two, served at six different lighthouses, of which three were swept away while he was their keeper, during his lengthy career. In 1904, at Maryland Point light in the Potomac, he and an assistant were in the lighthouse when piled-up ice completely wrecked it. The two men stayed and operated the bell and light by hand until ordered out by Coast Guard headquarters in Washington. They had to be taken off by sleigh.

The Benoni’s Point lighthouse – its proper name was actually the Choptank River light station, but few people ever called it that – was a familiar part of the Oxford-area scene for many years. It was located two miles south-southwest of Town Point, guarding the entrance to the Tred Avon and steering vessels safely past the rocks off Benoni’s Point. Another lighthouse was on Sharp’s Island, farther out in the Choptank.

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The glass for the lens was formed and machined in a specially designed factory – lost to bombing in World War II. Due to various reasons, it has never been replicated.

French physicist and engineer Augustin-Jean Fresnel developed the multi-part Fresnel lens for use in lighthouses. His design allowed for the construction of lenses of large aperture and short focal length, without the mass and volume of material that would be required by a lens of conventional design. A Fresnel lens can be made much thinner than a comparable conventional lens, in some cases taking the form of a flat sheet. A Fresnel lens can also capture more oblique light from a light source, thus allowing the light from a lighthouse equipped with one, to be visible over greater distances.

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The first-order Fresnel lens was the largest of the Fresnel lenses and could exceed 12 feet in height and one ton in weight. Because of their size and strength, these lenses primarily were used in lighthouses that needed an extremely focused and far-reaching signal. These lights were usually utilized in lighthouses along oceans.

This necessity brought about the creation and design of many lighthouses on the coastlines, which would let ocean navigators see when they were getting too close to dangerous outcrops. The issue was, the lights were essentially a large candle or oil lamp, and many times they were so dim that when the boat Captain saw the light, it was already too late. So scientists of the day searched for ways to focus and project the light much further.

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