““His system of equations worked with jewelled precision. Its construction had been an immense feat of sustained creative effort in three stages spread over 9 years. The whole route was paved with inspired innovations but from a historical perspective one crucial step stands out-the idea that electric currents exist in empty space. It is these displacement currents that give the equations their symmetry and make the waves possible. Without them the term @E/@t in equation (4) becomes zero and the whole edifice crumbles.””
