NEWBURYPORT — The fourth order Fresnel lens, a guiding light and beloved piece at the Custom House Maritime Museum since the late 1970s, will soon return to its original home at Pomham Rocks Lighthouse in Riverside, Rhode Island.

A Fresnel lens — pronounced "fray-NEL" — is a compact, multiprism lens used in lighthouses. The glass lens, divided into different sizes known as "orders," was developed by French physicist Augustin-Jean Fresnel. 

The first order lens is the largest and most powerful, while the sixth order is the smallest and better serves harbors and other smaller bodies of water.

The Pomham Rocks Lighthouse was first lighted on Dec. 1, 1871, with a sixth order Fresnel lens featuring a fixed white light. The color was changed to a fixed red about a year later.

The lighthouse, located on a half-acre island on the Providence River, provided navigational assistance to ships destined for Providence during the 19th century, according to the museum.

The sixth order Fresnel lens was upgraded to the fourth order lens in 1926 and remained in Rhode Island until June 1974 when the lighthouse was decommissioned by the U.S. Coast Guard. 

Prior to the Coast Guard taking over operations in 1956, Pomham Rocks Lighthouse was maintained over the years by six civilian lightkeepers.

Though the lens has been on display at the Custom House Maritime Museum at 25 Water St. for several decades, it is actually on loan from the Coast Guard. 

The Friends of Pomham Rocks Lighthouse, a 501(c)(3) nonprofit organization, was established in 2004 and has worked to raise money and secure grants to restore the Rhode Island lighthouse. 

The museum heard about these efforts and is working with the Coast Guard to return the lens to its original home.

Installed in the downstairs hallway of the museum, the Fresnel lens can be seen at night by passersby on the Newburyport boardwalk and by boaters on the Merrimack River. 

"It's wonderful that we have it," said Joan Whitlow, executive director of the museum.

Though it will be tough for the museum to say goodbye, volunteers and staff members know that Rhode Island is where the lens is meant to be, she said.

Moving the roughly 300-pound lens from Newburyport to Rhode Island will require some strategy, though, Whitlow added.

The lens will need to be disassembled and reassembled by a professional Coast Guard lampist, one of only six skilled artisans in the country who can perform such a highly specialized procedure, according to the Friends of Pomham Rocks Lighthouse.

For now, the lens will remain on display through the summer for visitors to check out and learn more about its history in Newburyport and Rhode Island. 

The Friends of Pomham Rocks Lighthouse has plans in the works to commemorate 150 years since the initial lighting of the lighthouse. 

To learn more about the efforts of the nonprofit and other events related to this commemoration, visit www.pomhamrockslighthouse.org

For more on the history of the lens at the Custom House Maritime Museum, go to https://customhousemaritimemuseum.org/fresnel-lens/.

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