By Rachel Balderson

 

Over many centuries, lighthouse technology has continuously evolved and improved. Although the earliest known lighthouse dates to the Egyptians in 280 B.C., European style lenses were first invented in 1810 and consisted of thick, poor quality glass that gave the beams of many lighthouses a ‘muddy’ appearance. In 1811, Lecoat de Saint-Haouen, the chief of staff of the French Imperial navy, proposed coordinating lighthouse signals along the coast in order to regulate a system for sailors. Because of this initiative, the Lighthouse Commission was born on April 29, 1811. François Arago (1786-1853), a professor at the Ecole Polytechnique, took leadership of the Commission in 1813 and in 1819 requested Claude Mathieu and Augustine Fresnel to be his coworkers on a project to review possible improvements to lighthouse illumination.

Augustine Fresnel (pronounced Fre-nel) was born May 10, 1788 in Broglie, France, to a Jansenists family. This Roman Catholic reform movement was established by Cornelius Otto Jansen who believed the destiny of an individual’s afterlife was predetermined despite actions taken throughout life. These beliefs strongly influence Fresnel during his lifetime. After the French Revolution, the political situation in France was tumultuous and caused his father’s construction work to cease. The Fresnel family moved to the village of Mathieu, where Fresnel’s education was continued at home. At age 12, Fresnel began studying at Ècole Centrale in Caen where he first became interested in science and math. At age 14, he entered Ècole des Chaussees, the oldest civil engineering school in the world, and completed a three-year course that certified him as a civil engineer. While working on engineering projects he began to take on science projects in his spare time and became interested in light in 1814. 

In 1815, when Napoleon escaped his exile in Elba, Fresnel left his engineering job to pledge his allegiance to the King, Louis XVIII. After the success of Napoleon, Fresnel was put under police surveillance and had to return to his home in Mathieu. There he was able to focus on light experimentation and wave theory in particular. His use of mathematical analysis disproved many popular objections that other scientists had used to discredit the theory. In 1819, the Academie des Sciences announced that the Grand Prix would be awarded to the scientist with the best work on diffraction. Fresnel took this opportunity to explore his theory of diffraction as well as promote his work with wave theory. Fresnel was awarded the Grand Prix from a committee that François Arago sat on, which introduced him to the Lighthouse Commission. In 1823, Fresnel was elected to the Academie des Sciences as well as the Royal Society of London, from whom he received a Rumford Medal in 1827. Tragically, Fresnel died of tuberculosis in 1827 at age 39.

 

Throughout Fresnel’s time in the Lighthouse Commission he drew from the work of researchers Buffon and Condorcet. Georges de Buffon, also known as Georges-Louis Leclerc, was an eighteenth-century historian, mathematician and scientist. He studied at Angers University but was expelled after participating in a duel. His interest in natural phenomena led to his study of light, mirrors, and lenses. He pioneered a method of constructing concave mirrors that is still used to this day. In 1748 he discovered that only the outer surface of a lens is necessary for bending light, a concept that transformed the construction of lighthouse lenses and reduced their cost. Buffon died in 1788 in Paris. The Marquis de Condorcet was the first person to suggest that one could build up the lenses using separate pieces versus using one large, thick piece of glass. It was said that it was not possible to grind a single piece of glass the way Buffon proposed or to create the series of one-piece rings that Condorcet proposed. 

Fresnel first fabricated his lens in 1822 and it was first used in 1823 to guide mariners through the Dordogne River in Southwest France. A Fresnel lens is composed of hundreds of pieces of deliberately cut glass in the design of a barrel or beehive. It consisted of eight bull’s eye flash panels, which refract light that would normally scatter in both vertical and horizontal patterns into one intense beam of light. He then added eight trapezoidal lenses at a 25-degree angle above and below the flash panels to collect the light above the burner or flame and direct it to eight large mirrors that reflected the light horizontally above the main bull’s eye panels. These trapezoidal lenses were able to increase the duration of the flash by almost double that of the main lens panels alone. He then took this basic design and flipped it on its vertical axis to create the first fixed lens in 1824. This included twelve vertical panels in a circle to create a flat disc shape allowing the mariner to see a constant light versus a flash. In 1825, Fresnel combined the two, adding flash panels to the fixed lens causing mariners to see a fixed light followed by a bright flash of light.

Each lighthouse has a unique signal they portray using a system of flashes allowing mariners to identify different lighthouses that are in close proximity. Before automation, a clock-like mechanism was wound by hand every few hours to make the flash panels rotate around the lamp to produce the flash effect. The New Cape Henry Lighthouse uses Morse Code for the letter ‘U’, (dot dot dash), as it’s signature flash pattern. 

In 1857, the old lamp system in the Old Cape Henry Lighthouse was replaced with a Second Order Fresnel Lens which was approximately 6.5 feet tall and a little over 3,500 pounds. It was able to cast its light 15 miles out to sea. The New Cape Henry Lighthouse was fitted with a First Order Lens when it was commissioned in December of 1881. This lens is still in use to this day, and its light can be seen from 19 miles away. The New Cape Henry Lighthouse was outfitted with a 2p Lamp Changer and LED optic bulb so that when one bulb burns out it will automatically switch to the other bulb with no interruption in light. Despite these new advancements, the light would not be the same without the aid of its original Fresnel lens. Augustin Jean Fresnel and the invention of his lens changed the course of naval navigation and saved the lives of countless mariners throughout the years.

 

Bibliography

Gaal, R. (2016). July 1816: Fresnel’s evidence for the wave theory of light. American Physical Society. Retrieved April 3, 2023, from https://www.aps.org/publications/apsnews/201607/physicshistory.cfm 

O’Connor, J. J., & Robertson, E. F. (2002). Augustin Jen Fresnel. MacTutor. Retrieved 2023, from https://mathshistory.st-andrews.ac.uk/Biographies/Fresnel/ 

Tag, T. (n.d.). The Fresnel lens by Thomas Tag. The Fresnel Lens by Thomas Tag | US Lighthouse Society. Retrieved April 3, 2023, from https://uslhs.org/fresnel-lens 

U.S. Department of the Interior. (2019). Fresnel lens (U.S. National Park Service). National Parks Service. Retrieved April 3, 2023, from http://www.nps.gov/articles/fresnel-lens.htm