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This spring marked the return of something that has been missing from Wisconsin's Pottawatomie Lighthouse on Door County's Rock Island for more than 40 years: a fourth order Fresnel lens.
The original lens has been missing since the early 1960s when the Coast Guard replaced it with an automatic beacon that was attached to the lantern deck. The old lens was crated up and stored in the basement. Some time later, it disappeared and its whereabouts have remained a mystery ever since.
Friends of Rock Island (FORI) members have been trying to track down a replacement for years. The group's secretary, Colleen Andrews, came upon a website last fall advertising replica lenses for sale.
Kirby Foss, property manager of Rock Island State Park, was contacted about this find. He was eager to have a lens put back in the lighthouse as well. The wheels of government began turning and soon the Friends were writing a matching grant to the Department of Transportation, which the DNR helped to facilitate. A contribution of $5,900.00 from the non-profit organization covered 20% of the $18,900.00 lens plus additional funds for a cast iron pedestal, delivery, and installation charges.
With the funding secured, the DNR contacted Dan Spinella, an engineer from a company called Artworks Florida. Spinella carefully researched the specifications of the original Fresnel lens from the Pottawatomie Light. He then furnished Gary Knappenberger of Enberg Mold and Tool in Jacksonville, Florida, with a CAD drawing.
It took Knappenberger about six weeks to manufacture the replica lens made of a 3/8” brass framework and
hand-polished acrylic prisms. The prisms were then arranged in the framework according to formula first developed by Augustin Fresnel, the French physicist who invented the lenses back in the 1800s. Such an arrangement allows for light to be refracted, reflected, and sent out through the dioptric portion of the lens.
Knappenberger delivered the lens to Rock Island on May 10, along with Ed Gunn, director of operations at the Ponce DeLeon Inlet Lighthouse in Florida, and
Nathan Gunnlaugsson.
The three men carefully hoisted the lens up the three narrow stairways of the lighthouse tower just barely managing to squeeze it through the hatch opening and into the lantern room. There it was placed on a cast iron pedestal where it will be used as an interpretive tool when visitors tour the station.
The Friends of Rock Island will be sharing this
optical beauty with visitors every Monday through Saturday from 10:00 AM to 4:00 PM starting Memorial Day weekend and continuing until Columbus Day. For more information, visit http://fori.us.
This story appeared in the
July 2005 edition of Lighthouse Digest Magazine. The print edition contains more stories than our internet edition, and each story generally contains more photographs - often many more - in the print edition. For subscription information about the print edition, click here.
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