An engineer of the ancient world would have gone slowly mad trying to understand how a solid roadway could be fixed at both ends while its centre travelled at a hundred miles an hour... The corridor still inclined upwards, and in a few hundred feet had curved through a complete right-angle. But only logic knew this: to the senses it was now as if one were being hurried along an absolutely level corridor. The fact that he was in reality travelling up a vertical shaft thousands of feet deep gave Alvin no sense of insecurity, for a failure of the polarizing field was unthinkable. (en)