An authentic narrative of the loss of the American brig Commerce : wrecked on the western coast of Africa, in the month of August, 1815, with an account of the sufferings of the surviving officers and crew, who were enslaved by the wandering Arabs, on the African desart, or Zahahrah : and observations historical, geographical, &c. made during the travels of the author, while a slave to the Arabs, and in the empire of Morocco /