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.

Professor Green sighed in a sad but patient spirit. He could not help being a little disappointed even with the most intelligent outsiders with whom he conversed. Their remarks were pointed but hardly to the point. He felt more and more that he really preferred those who made no remarks. The flowers and the trees made no remarks; they stood in rows and allowed him to lecture to them for hours on the fallacies