Once, they were the height of lighthouse technology - large, beehive-shaped arrangements of hand-cut prisms that could magnify the weak glow of an oil lamp into a beam of light that stretched 20 miles out to sea.
Although modern technology has replaced many Fresnels, the gemlike lenses that once were cutting-edge are viewed as valuable - maybe even priceless - works of art. And a few of the more neglected Fresnel lenses are being restored in Maryland.
The move to restore Fresnel lenses for public display is part of the Coast Guard's efforts to preserve lighthouses and celebrate their place in Americana.
"Lighthouses are America's castles. They are unique, and they are part of our maritime heritage," said Joseph S. Cocking, a Coast Guard chief warrant officer in Miami who is one of four Fresnel lens experts in the country. "And [Fresnel lenses] are the heart of the lighthouse."
Like giant diamonds, each Fresnel lens is unique. Because the prisms - sometimes more than a thousand per lens - are no longer manufactured, the lenses are difficult and sometimes impossible to repair. As a result, the Coast Guard says, they are virtually priceless.
On a recent morning at a cluttered Coast Guard warehouse in Forestville, pieces of one of the larger Fresnel lenses are scattered on tables, crates and large warehouse shelves among other Coast Guard artifacts such as ship wheels, lifejackets and brass bells. The lenses were primarily produced in six sizes, called orders, first-order lenses being the largest.
This first-order lens, originally a beacon that guided sailors in the Florida Keys, languished in poorly packed crates in a boiler room at the Coast Guard Academy in New London, Conn., for more than three decades after being removed from the lighthouse.
Many of the greenish, triangular prisms are severely chipped. A few are broken and unusable. A significant portion of the prisms have fallen from their positions as the tarnished brass frames warped and the more-than-century-old caulk that held them in place crumbled.
That makes the task before the volunteers from the Chesapeake Chapter of the U.S. Lighthouse Society even more difficult. Each prism is uniquely cut and so fits into only one of almost 600 similarly shaped slots.
When the volunteers determine where the prism fits into the lens, they wedge pieces of Popsicle sticks - a modern replacement for the small wood wedges used originally - between the prism and the frame to hold them tight.
They then apply caulk to secure the prism, making sure it is level with the frame so that the more than 40 panels can eventually fit snugly together.
When fully assembled, this first-order lens will stand about 8 feet tall and 6 feet wide, and will weigh about 3 tons. But that could be a long way off.
On a nearby shelf are several assembled panels of a slightly smaller, yellowish, second-order lens, originally from the Moose Peak Light in Maine, that are expected to be displayed at the Maine Maritime Museum in Bath. It took a half-dozen volunteers, who came once a month, more than two years to complete that lens.
"It is a slow process; it just takes time," said Tom Wade, education coordinator for the Chesapeake Chapter of the U.S. Lighthouse Society and one of the Fresnel lens volunteers. "You can't rush it. You can't use shortcuts."
For lighthouse enthusiasts such as Wade, who said he has been "fascinated with lighthouses for years," the opportunity to work with Fresnel lenses is rewarding.
"It's my way of getting involved in the preservation of the lights we do have," he said.
Invented by French physicist Augustin Fresnel in 1822, Fresnel lenses were technological marvels that revolutionized maritime travel. They could produce light four to five times stronger than that produced by the previous mirror systems.
They were first installed in U.S. lighthouses in the 1850s and maintained their pre-eminence well into the 20th century. Even after lamps that once burned whale oil were replaced with electric bulbs, the Fresnels, shaped like beehives or bulls-eyes, remained in use.
But when the Coast Guard ended the era of the fabled lighthouse keeper and began automating lighthouses, the fragile Fresnel lenses were endangered. Cocking said they can be fractured, when active, by the oil from a fingerprint drawing heat to the glass.
Some, like the lenses at the Turkey Point Light in Cecil County and the Hooper Island Light in Dorchester County, were stolen. Others were shot out as someone took aim at the giant glass bulls-eye or smashed to pieces by vandals, including one at the Sandy Point Shoal Light near Annapolis.
Some were discarded
In the 20th century, Wade said, unknowing Coast Guardsmen, unwilling to lug away the heavy Fresnel lenses, tossed some overboard when they replaced them. "It kills us now" to think about that, Wade said.