Birket-Smith, K. 1937. Ragnar Numelin: The Wandering Spirit. A Study of Human Migration. With a Foreword by Dr. Edward Westennarck. H. Hagerup, Copenhagen, Macmillan & Co., London. 1986.875 sider 18 x 26 cm. Pris 20 Kr. Geografisk Tidsskrift - Danish Journal of Geography. 40, (Jan. 1937).