"Circularity is a powerful concept, the idea of a closed loop even more so. In circular motion there is magic, just as there is in electro-magnetism. But it only manifests itself when it is, like (shall we say for the moment, rather than a 'reflection' of) its 'neighboring head', truly three-dimensional. ...We can induce current into the one [coil] from the other by means totally unintelligible to us, but to which we give the name . But if I place one coil with its axis at right-angles to that of the other, there is no induced voltage. It is as if the two circuits lived in different worlds... What is the meaning of perspective in a four-dimensional space?"