You Thought It Was Safe to Go Back Into the Gallery . . .

Two centuries before the film “Jaws” started breaking box-office records, a Boston artist captured the horror and fascination of sharks in a landmark painting.

Now the National Gallery of Art has a special show to help explore the mysteries of how an American painter in Britain portrayed a scene in Cuba, possibly after Dutch and Italian models.

Nicolai Cikovsky Jr., curator of American and British painting at the gallery, called “Watson and the Shark” one of the great paintings in the history of art.

The painting, almost life-sized, shows a key event in Watson’s life. A sailor at the age of 14, he went for a swim in Havana harbor and a shark so mauled his leg that it had to be amputated below the knee. Rescuers are shown reaching out to drag him into their boat, just as the shark attacks again.

Copley’s painting occupies a place in the development of American art that can be compared with that of the Boston Tea Party in American history. There’s a connection, too.

John Singleton Copley went from Boston to London at the age of 36 on the eve of the American Revolution. He had painted such soon-to-be heroes as Paul Revere and John Hancock, the first signer of the Declaration of Independence. Though he apparently had some sympathy for the revolution, Copley lived the rest of his life in Britain.

Shortly before his arrival in London, his brother-in-law, Jonathan Clarke, and the man who was to be the subject of Copley’s painting, Brook Watson, sent a shipment of tea to Boston. Americans protesting against a British tax dumped it into the harbor, a demonstration that led to the War of Independence.

Watson, by the way, recovered from the attack, prospered as a businessman and became Lord Mayor of London.

Now for the mysteries.

Why did Copley treat such an unusual subject at all? And why on such a large scale, nearly seven feet by five feet? No bill for the picture has survived, nor any letters about it.

Who is the black sailor in the boat of rescuers and why is he there? Copley later did a portrait of the same man, described then as “a Favourite Negro.” That may have meant he was in Copley’s household. But nobody knows. Among the theories:

* He was included as a protest against slavery.

* Watson wanted a black man in the picture for the sake of realism, or because one of the sailors in the boat actually had been black.

* Copley wanted a black (an early sketch for the picture shows the figure as white) to give an exotic touch to the atmosphere.

Is there a religious meaning to the picture?

Some writers have made a connection between the three attacks on Watson by the shark, the three days reported in the New Testament between the Crucifixion and Resurrection of Jesus, and the three days the Old Testament says Jonah spent inside the whale.

Is there some symbolic reference to the American War of Independence? One scholar has suggested that the loss of Watson’s leg symbolizes the dismemberment of the British Empire. Others find that far-fetched.

Where did Copley get his ideas?

He owned an engraving of Peter Paul Rubens’ “The Miraculous Draft of the Fishes,” a portrayal of one of Christ’s miracles. He may have seen a drawing of the same subject by the Italian master Raphael. Both are scenes of people in small boats, resembling the one Copley painted.

The show will run at the National Gallery until April 11. It already has been seen in Detroit, and will be at the Boston Museum of Fine Arts May 13-Aug. 1.