TRAVELLERS in the Middle Ages were not the sticklers for truth they perhaps tnight have been. Nevertheless, their fantastic angle of vision, however much it may have impeded knowledge at the time, has the merit of providing us today with amusing, as well as instructive, reading—instructive, because of the light it throws on the Middle Ages' mentality and amusing, because of the grotesque vein of superstitious credence with which it is threaded. In this weekly series, travel books of all times will be discussed, from Marco Polo and Sir John Mandeville to D. H. Lawrence and Dr. Ethel Smyth. Miss Grierson, who is giving the series, is the daughter of Professor Grierson, of Edinburgh. She has several times deputised before the microphone for Mr. Desmond MacCarthy.