The professor had begun, as he always began, by saying that it was quite easy to explain; which was doubtless true, as he was always explaining it. But he often ended by affirming fallaciously that it was quite easy to understand, and it would be an exaggeration to say that it was always understood. Anyhow, he was just about to read his great paper on his great theory at the great Astronomical Congress that was to be held that year at Bath; which was one reason why he had pitched his astronomical camp, or emplaced his astronomical gun, in the house of Farmer Dale on the hills of Somerset. Mr. Enoch Oates could not but feel the lingering hesitation of the landlord when he heard that his protégés the Dales were about to admit an unknown stranger into their household. But Pierce sternly reminded him that this paternal attitude was a thing of the past and that a free peasant was free to let lodging to a homicidal maniac if he liked. Nevertheless, Pierce was rather relieved to find the maniac was only an astronomer; but it would have been all the same if he had been an astrologer. Before coming to the farm, the astronomer had set up his telescope in much dingier places--in lodgings in Bloomsbury and the grimy buildings of a Midland University. He thought he was, and to a great extent he was, indifferent to his surroundings. But for all that the air and colour of those country surroundings were slowly and strangely sinking into him. “The idea is simplicity itself,” he said earnestly, when Pierce rallied him about the theory. “It is only the proof that is, of course, a trifle technical. Put in a very crude and popular shape, it depends on the mathematical formula for the inversion of the sphere.” “What we call turning the world upside-down,” said Pierce. “I’m all in favour of it.” “Everyone knows the idea of relativity applied to motion,” went on the professor. “When you run out of a village in a motor-car, you might say that the village runs away from you.” “The village does run away when Pierce is out motoring,” remarked Crane. “Anyhow, the villagers do. But he generally prefers to frighten them with an aeroplane.” “Indeed?” said the astronomer with some interest. “An aeroplane would make an even better working model. Compare the movement of an aeroplane with what we call merely for convenience the fixity of the fixed stars.” “I dare say they got a bit unfixed when Pierce bumped into them,” said the Colonel.