The modern world was created by the drifting of the continents, says the theory of plate tectonics. Thus the Atlantic Ocean has widened, and is continuing to do so, as America and Europe drift apart. So, says Daedalus, why have the Atlantic cables not snapped? Presumably because the drift is very slight, a few centimetres a year, and is well within the elastic stretch of a few thousand kilometres of cable.

Nonetheless, a transoceanic cable is a perfect electrical strain gauge. The resistance of the Atlantic cables must be rising as their conductors lengthen and their conductive cross-section falls. Other oceanic cables span the Pacific, the Indian Ocean and so on. They may be shortening as their paths slowly decrease, so their resistance should be falling. Many of these cables were laid in the days of telegraph and low-frequency telephone traffic. It would cost little to take them out of service for measuring, and transfer their burden to modern high-frequency or fibre-optic cables.

So here is a splendid way of checking the theory of continental drift. The world is bound by many cables, and the ships that laid them were navigated carefully and have left detailed logs. The only snag is that the resistance of a single cable cannot be measured. You need at least two, there and back. They must be joined, and their final termination must be coupled by an excellent conductivity bridge.

Sadly, you cannot tell where or how evenly over its length the multiple cable is being stretched. A large extension in a small region (say, where plates are separating) has the same effect as a slight stretch maintained over many kilometres. Daedalus will be pleased by a change in resistance of a few parts per billion. A continuous watch will show whether the movement is slow and steady, or occurs in sudden jerks, possibly with oscillations about each burst of movement.

DREADCO communications engineers are now seeing which cables can be coupled into useful pairs or triangles. To provide a good test of current theories, each such multiple must allow an accurate measure of its round-trip resistance. The engineers may include long pipelines in their list, provided their resistance is also well defined. Railways usually maintain signalling and power currents which would interfere with the measurements. The whole experiment gives a cheap and novel way of testing one of the boldest theories of modern geology.