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 her surviving officers and crew, who were enslaved by the wandering Arabs, on the great 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 /