Harriet Martineau (the feminist and thinker 'who made the nineteenth century the dawn of freedom for half the human race') was certainly the most intelligent woman of her time, and she argued with uncompromising logic (which led her to abandon all religious faith, for instance). Between 1834 and 1836, Martineau travelled throughout America, interviewing everyone she met, from the President down to a black slave girl. On her return she wrote...