Letter from [John Ambrose] Fleming, FRS, to James Mackenzie Davidson Discusses the fact that submarines cannot transmit wireless signals when submerged. Directs Mackenzie Davidson towards Chapter Nine of his book 'Electric Wave Telegraphy', in which he he explains that electric waves can glide over sea water, as the sea is a good conductor, however, cannot penetrate it because, like all good conductors, it is opaque [and so the waves are absorbed]. 16 June 1917