the British Isles. Fish and electricity A particularly important research finding took place in 1950. The previous year, on a visit to London Zoo, Lissmann had noticed that the African knife fish (Gymnarchus) was able repeatedly to swim backwards at the same speed and with exactly the same corporeal dexterity around obstacles in its fish tank as when it swam forwards, while avoiding collision. He inferred that the fish must have what in human terms would be seen as some form of "sixth sense", something which he also thought he detected in the electric eel in another aquarium tank nearby: he thought the phenomenon might well involve electricity. Towards the end of 1949 Lissmann married, and as a wedding present from one friend he was given his own knife fish, which he now went on to study in his laboratory. He placed the fish in a large fish tank into which he inserted electrodes. With these he was indeed able to detect a naturally occurring electric current emanating from the fish, albeit a current far too weak to be felt by a person. He then found ways to increase the current to a point where it could be measured with a conventional oscilloscope. One story - not universally accepted - reports that the fish generated a measurably increased electrical charge when a student combed her hair beside the fish tank. The fish died soon after this, but replacements were acquired, and working with his exceptionally capable research assistant Kenneth E Machin (1924-1988), whose PhD had covered radio-astronomy, Lissmann was able, through observation and measurement, to demonstrate that the variable electrical charge was produced by the knife fish itself, and that the fish reacted to any change in the electric field around it, even when produced close to, but outside, the fish tank itself. They were helped in their work by a perspex model of an African knife fish constructed by Ken Machin, with two electrodes attached to it permitting the perspex fish to generate an electric field equivalent to that produced by the real fish. Machin struggled and failed to produce for the perspex fish an intricate variability in the strength and shape of its magnetic field comparable to the produced by the real fish, but observations involving the perspex fish nevertheless provided a large additional amount of valuable data. A key conclusion was that the African knife fish was