Many reactors circulate their molten sodium coolant by an electromagnetic pump. A current passes through the molten metal at right angles to an applied magnetic field, and the motor effect impels the sodium at right angles to both. Daedalus reckons it would work with insulating fluids too. For a voltage applied across an insulator shifts its electrons transiently, as the insulator becomes polarized. Remove the voltage, and they would move back again. In a steady magnetic field, these two brief opposite ‘displacement currents’ would exert a push and then a cancelling pull on the dielectric. But reverse the magnetic field in the interval, and the dielectric would feel two pushes in the same direction — a true motor effect.

So, says Daedalus, put an insulator in a.c. electric and magnetic fields at right angles, reversing at the same frequency and the right mutual phase, and it will feel a cumulative force. At first he hoped that the whole thing could be driven as a resonant circuit, with the insulator as the dielectric of its capacitor, and the inductor providing the magnetic field; but the phasing comes out wrong. The two fields will have to be created and phased by special circuitry.

The obvious working fluid for the new pump is air. Fans, propellers, blowers and jet engines are all noisy, complicated devices. A simple silent air-pump with no moving parts would be widely welcomed. For maximum thrust, it should work at the highest feasible frequency — many megahertz if possible. Daedalus's first product will be a little cooling blower for computers and electronic gadgets. But he soon hopes to scale it up. Displacement-current pumping could make all sorts of blowers, compressors, air-conditioners and fans blissfully silent and reliable.

His ultimate goal is a displacement-current aircraft engine. The entire craft would have to be designed around this radical new source of thrust. Its fields would enclose as large a volume of air as possible, so that even a gentle induced flow moved a lot of air. An electromagnetic helicopter with vertical downflow might fill the bill. The strength and direction of thrust could be altered at electronic speed, giving the craft a wonderful agility in the air. And its total silence would be welcomed both by the crew and the long-suffering aerophobic public.

The Further Inventions of Daedalus is published by Oxford University Press.