LITTLE BREWSTER ISLAND — Last summer, a Coast Guard officer was taking a tour of Boston Light when a particular artifact caught his eye.
There are a lot of old things at Boston Light — home of the nation’s first and oldest light station, built in 1716 a mile off the coast of Hull — but one artifact seemed old in a particular way.
The item in question was a 293-year-old fog cannon, which for the first 150 years of its life was fired every 30 minutes during periods when poor visibility limited the reach of the light. The officer, Captain James McPherson, wondered whether it might just be the oldest artifact in the entire Coast Guard.
Thus began a historical mystery hunt, as Coast Guard historians and archivists worked to answer that question and others, such as making sure the long black cannon on display was the original and that it has always been owned by one of the entities that would form into the Coast Guard.
After a few months of work, the Coast Guard determined that McPherson’s hunch was right. The signal cannon was purchased in 1719 by the Lighthouse Service, which later became part of the Coast Guard, making it the oldest known artifact by several decades.
‘There was quick concurrence from everyone involved in this.’
The lighthouse itself was older by three years, but was torched by the British as they left town on what is now known as Evacuation Day, March 17, 1776. The original tower was financed by a penny-a-ton tax on all ships entering and leaving Boston Harbor.
“Sometimes maritime historians have a lot of debate over firsts and lasts and whens, but there was quick concurrence from everyone involved in this,” said Lieutenant Joe Klinker, a Coast Guard public affairs officer who worked on establishing the cannon’s provenance.
On Friday, Rear Admiral Daniel Abel, 1st Coast Guard district commander, visited Boston Light to see the cannon and present a commendation to Sally Snowman, the 70th lighthouse keeper at Boston Light and the first female.
Snowman said the fog cannon was the brainchild of the third keeper at Boston Light, John Hayes, who noted that the bright light — which can be seen 27 miles out — was of little use in thick fog.
He asked for, and was granted, permission to buy a cannon.
The cannon remained in service until 1851, when it was replaced by a large fog bell.
Today the lighthouse uses an automated system that measures the thickness of the fog and releases bursts from an air horn at intervals that indicate that thickness to mariners.
Friday marked the start of the tourist season at Boston Light, as the first boat of visitors found themselves walking into a small ceremony to commemorate the discovery.
Since 1999, when the National Park Service began a pilot program to bring visitors to the island, more than 23,500 people have made the trek, which includes the opportunity to climb the 76 steps to the top of the light station tower for a close-up look at a classical Fresnel lens, a French engineering marvel from 1859 that is still in use today.
“We let tourists come up here?” Abel said as he ascended the narrow steps for his first look at the Fresnel 102 feet above.
They do, and the hope is to bring even more up the tower this year by moving the location for the ferry to a tourist-heavy spot near the New England Aquarium.
Snowman, who dresses in 1783 garb to commemorate the year the commonwealth rebuilt the tower that had been blown up by the retreating British, is the last Coast Guard lighthouse keeper in the country, a job she has held since 2003.
The light itself is automated — it was the last in the United States to do so. Snowman, a 60-year-old from Plymouth, spends long periods in the keeper’s house, particularly in the warmer months, and she and members of the Coast Guard Auxiliary take care of the maintenance.
On Friday, with the first guests arriving for the season, she spent the morning baking cookies.