The Time Traveller was explaining a strange idea to us. We sat round the fire in his comfortable house, and the light shone on the glasses in our hands. "You must listen carefully," he said. "I shall have to argue against ideas that everybody accepts. There are really four dimensions, not three. We call them length, width, height — and duration. Your body moves through space, and it also moves through time, from the moment you are born to the moment you die. There is no difference between time and any of the three dimensions of space, except that our minds move along it. Some people have almost seen this, but nobody has thought of the next step." "And what is the next step?" asked the Psychologist. "If we can move up and down in space, and from side to side, why can we not move backwards and forwards in time?" said the Time Traveller. "I have been working on a machine that will travel in any direction of space and time, as the driver of it may choose."