Records of Humber Conservancy and the Humber Ports (Records deposited by Associated British Ports and its Predecessors) > Humber Conservancy > Publications produced, or acquired by the Humber Conservancy Board > International Lighthouse Conference, 1929 > Physical Principles governing the Design of Sound Signalling Apparatus of large output for use in Air and Water as an Aid to Navigation when visibility is bad by H. Hecht, Kiel