Watching black history emerge, subject by subject

So attests the catalog to ''Portraits of a People: Picturing African Americans in the Nineteenth Century," an exhibit of more than 70 paintings, photographs, silhouettes, and prints at the Addison Gallery of American Art in Andover through March 26. Could it be Hercules gazing warily from the painting ''Presumed Portrait of George Washington's Cook"? It is traditionally attributed to Gilbert Stuart, but the painting's authorship and the identity of the sitter are as fugitive as Hercules himself.

Like Hercules's story, much of the history of black people in early America was lost or only cursorily recorded by the dominant, racist white culture. Slavery in America is thought of as a Southern scourge, but until the early 19th century it was practiced in the North as well. The Northern variety has often been described as kinder than its Southern counterpart, but little evidence supports this. Numerous accounts tell of Northern masters freeing slaves late in life, seemingly a kindness, when in fact they were often abandoning them so they wouldn't have to care for them in their old age.

In 1641, Massachusetts became the first British colony in North America to recognize slavery as a legal institution. By 1770, some 5,000 black slaves resided here. Among them was Phillis Wheatley, ''Negro servant to Mr. John Wheatley, of Boston," as printed around her engraved portrait in the frontispiece to her 1773 collection of poems.

Wheatley was the first black person from New England to have her poetry publicly published in English and the first American woman to have her likeness printed with her writings. Her success helped win her freedom. Her portrait (attributed to Scipio Moorhead, another Boston slave) is so familiar from schoolbooks that it's startling to see the real thing here and find how rich it is in person.