Chicago’s Lighthouse


Fresnel Lighthouse Diagram

The Columbian Exposition, held in Chicago in 1893 was felt to be the ideal setting for the Lighthouse Board to demonstrate its progress in developing advanced navigational lighting technology. That technology centered around the Fresnel lens. A Fresnel lens can capture light from any source and direct that light into a narrow focal beam that is visible at great distance.

A Fresnel lens is much lighter and smaller than conventional lighthouse lenses. Developed by the French and first used in 1823 at the Cordouan lighthouse in France, Fresnel lens technology was constantly being improved upon by engineers throughout the world.

While the glass making technology and lens polishing didn’t require exotic skill, the Fresnel lens required a high degree of engineering. This made these lenses very valuable and very rare. During the American Civil War, the capture and occupation of lighthouses was a high priority for union naval forces. The union side dominated the seas during the war, leaving the Confederacy to concentrate on breaking naval blockades to afford passage of vitally needed supply ships.

Along the coasts of those states that had seceded, union naval forces often tried to keep many of the lighthouses operational while the confederates tried to keep them dark. The most effective method employed by rebels and rebel sympathizers was the removal of the Fresnel lens from the lighthouse. But respecting the value of these lenses, both sides were loath to simply destroy them. Instead, they were often carefully removed and hidden by one side or the other, most making their way back to their original place following the end of the war.

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Posted by on Mar 1st, 2013 and filed under Feature Story. You can follow any responses to this entry through the RSS 2.0. Both comments and pings are currently closed.

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