Gould piloted the Africa from New London to the Cape Verde Islands off the African coast in about 50 days, looping across the Atlantic in a slightly downward curve and working his way from "fresh gales with snow" to "fresh breises and hazey" off the islands. The men caught a sea turtle and hauled it on board, fresh food by that point in the voyage a great luxury, but the turtle was already dead, "and stunke bitterly," Gould wrote.

The ocean crossing reads like the diary of Capt. Jack Aubrey in a Patrick O'Brian novel. The weather was often fierce, the navigator constantly checked his course, and the seamen worked like dogs - the phrase "Men Imploy'd" - appeared almost daily.

As the ship neared Africa, Gould took frequent depth soundings, checking the tallow at the end of the sounding rope for what its sandy debris would tell him. He described the look of the sea and its "colour," shifts in the wind and the deployment of the ship's sails in response to that wind. There were moments of hectic activity that echoed the terse entry I saw in the log of a New London whale ship: "All hands on deck, God damn you!"

The Cape Verde Islands where the Africa first dropped anchor was a slave-trading archipelago belonging to Portugal. It was March when Easton and Gould arrived, and they were racing against a clock because West Africa's rainy season - five months of torrential rain, hurricane weather and diminished trade - would begin in May.

A friendly bribe was sent ashore "for the Govenor" of St. Jago, the largest of the Cape Verde Islands, but the lumber and rum didn't seem to have done the trick, so Easton and his men headed for the Isles de Los, a small group of slave-trading islands north of the Sierra Leone River.

In Gould's highly phonetic style of spelling, the Isles de Los appear as the Edlesses. On some 18th-century maps, they are called The Idols, or Las Idolas, or even, movingly, the Isles of Loss.

At Isles de Los, there was plenty of socializing with other captains, an early form of networking essential for survival.

"At 3 p.m. arriv'd at the Edless & came to anchor off the White Rocks ... at 6 p.m. A Capt. Cassen & Docter Cooper, came abor'd."

The next day, "Blair McAdams came from Dorna in his shallop & Mr. Wallis's shallop from Dimbre But Brought No Trade."

The ship captains in Gould's log needed to know where it was safe to trade, which tribal people were at war, where enemy French ships had been seen, and where there were good supplies of prime slaves. In the most modern way, ships coming onto the African coast needed fresh information.

Given the potential for huge profits, the slave trade in Africa often turned deadly. Captains had to worry about mutiny and desertion, as well as disease and war. Their world was one of extreme, systemic violence, and it engulfed commanders and crewmen as well as their captives.

John Easton bought 10 people, four of them children, but trade was "dull," Gould wrote, and perhaps that prompted his captain to bring the Africa to sail on April 5, "Bound for Serrelone."

The Laird
Richard Oswald and Bunce Island

Scotsman Richard Oswald would not have been familiar with the term "vertical integration," but he knew that owning related businesses enhanced the bottom line. Bunce Island had been a slave-trading fortress for almost 80 years when he and five business associates in London bought it in 1748, but it hadn't yet made anybody rich, despite its ideal location.

Set in the Sierra Leone River at the precise limit of navigation for all but very small boats, Bunce sits in front of 600 miles of coastline punctuated by rivers that snake deep into the African interior. Black traders from the interior and coast would come to the island's southern side with slaves to sell, while larger ships from Europe and the American colonies sailed to its northern side to buy those slaves. Only 350 feet - about the length of a football field - separated the two sides.

By the mid-1700s, the slave castles were in decline. Virtually all the traffic was carried on by independent traders who would set up short-term trading posts along the West African coast. The thriving complex on Bunce was an anomaly, but a successful one.

Oswald made payments to the local king for the use of Bunce and property on several adjacent islands. On these other islands, Grant, Oswald & Co. built ships, grew food, maintained supplies of fresh water and wood, and conducted trade.

Though slaves were purchased from the African traders who came to Bunce, the Oswald company's men and ships - in what was called "the factory fleet" - also collected slaves from various points along the coast. They didn't wait for business to come to them.