If such warning is not given the absence thereof constitutes a trap, at any rate to persons who were made aware of the obstruction ... In order to keep wires clear of the water surface at jnid-span, 2J-in. pipe supports (from C to 16 ft. high) were set up just ... Looking back, the period from about 1928 to 1938 is seen to be one of great technical progress ; the following are among ... The appearance of the units and of the poles was in line with developments in industrial art in other spheres.