Dorothy Wickenden’s case study of Sally Snowman, the last lighthouse keeper in America, is the starting point of her journey into the history of the lighthouse keeper. A dangerous and lonely profession, it’s a fascinating one to honor before it finally goes extinct.

Commercial ship pilots tend to be hardheaded, by necessity, but even they say that lighthouses still have a place. Captain Brian Fournier learned his trade as a tugboat operator in Boston Harbor. “Boston Light was my back yard,” he told me. These days, he generally pilots oil tankers in Maine, and like other professional navigators he uses G.P.S. Still, he prefers to rely on the evidence of his eyes and the reassurance of a long tradition. In low visibility, Fournier said, “I’m looking for the flash of a buoy, the flash of the lighthouse.”