THE migrations of birds ' are not quite so much of a mystery as they used to be, but the more that is known of them, the more wonderful they seem. The bird-routes for the different seasons cross all Europe, Africa and Asia, North and South and East and West. In this talk Sir William Beach Thomas will describe these vast journeys, by which, for instance, a pair of swallows that nest in the eaves of a house in England may winter in mid-Africa.