The Nahant sea serpent: Marshal James Prince and Samuel Cabot at Long Beach, 1819

New England had serpent fever. In 1817 a creature off Gloucester drew a committee from the Linnaean Society of New England. In the summer of 1819 the sightings were back. Around 12 August a Mr. Smith said the serpent had been seen the previous evening at Nahant beach, on the coast north of Boston.

Then James Prince saw it. From a quarter past eight to half past eleven he watched from Long Beach through a telescope, his family beside him. He had seven distinct views. At some of them the animal was not more than a hundred yards away. Its head rose "about three feet out of water". "I counted thirteen bunches on his back: my family thought there were fifteen."

It passed three times at a moderate rate across the bay. It sank for about eight minutes at a time, and Prince guessed it rose to take breath. He judged it fifty feet long, sixty at most. His coachman called out, "Oh, see his glistening eye." More than two hundred other witnesses were watching. Prince's verdict was simple. "A harmless timid animal."

Samuel Cabot, a Nahant summer resident, watched from about 150 yards. The head "gave to my mind at the first glance the idea of a horse's head". It "moved his head from side to side as if to look about him". Behind it ran "eight or ten regular bunches or protuberances, and at a short interval three or four more". Then it moved faster, "causing a white foam under the chin, and a long wake". Cabot put it at "not less than eighty feet long". Around him stood "two or three hundred persons on the beach".

Prince dated his letter 16 August 1819 and sent it to Judge Davis, president of the Linnaean Society. The Boston Daily Advertiser printed it on 19 August. Cabot's own letter, to Col. Thomas Handasyd Perkins, is dated 19 August and appeared in Silliman's American Journal of Science and Arts in 1820. Perkins later summed up the Nahant witnesses. Fifteen to twenty three bunches. Eighty to a hundred feet. A colour "quite dark, approaching to black."

A later retelling adds a second scene. Two sentries at Fort Independence, on Castle Island in Boston Harbor, reported a sea serpent swimming past. Their superior, Col. Harris, confirmed it. One account dates this to 16 August 1819. Another gives 1818. No description of their own survives.

Not everyone was convinced. In 1819 the Charleston playwright William Crafts mocked the craze in The Sea Serpent; or, Gloucester Hoax, though his target was Gloucester, not Prince or Cabot. Writing about the Gloucester serpent in Skeptical Inquirer in 2019, Joe Nickell argued that a pod of narwhals had been mistaken for one animal, rising and falling in turn and lying still at rest. In 2023 Karl Brandt proposed a harpooned sperm whale still towing its hunters' overturned rowboat, the trailing debris looking like a line of humps. A large eel has been suggested too.

In 1892 A. C. Oudemans reprinted the letters in The Great Sea-Serpent, and they remain the core of the case. The Nahant Historical Society has shown affidavits and an illustration in its "Monstrous Sea Serpent" exhibit. And Amos Lawrence put it plainly. "I have never had any doubt of the existence of the sea-serpent since the morning he was seen off Nahant by old Marshal Prince through his famous masthead spy-glass."