He did not stop to solve any differential equations which would tell him the rock’s time of arrival; he threw power into the motors, turned the tank ninety degrees in a distance that threatened to twist off one of its treads, and got out from the mouth of the channel which was guiding the huge projectile toward him. Only then did he really come to appreciate the architecture of the city. The channels did not come straight into the open space, as he had noticed; instead, they were so arranged that at least two could guide a rock across any portion of the plaza. His action was sufficient to dodge the first, but it had been forseen; and more rocks were already on their way. For a moment he looked around in all directions, in a futile search for a position which was not about to be traversed by one of the terrible projectiles; then he deliberately swung the nose of the tank into one of the channels and started uphill. There was a boulder descending this one too; a boulder which to Barlennan seemed the biggest of the lot — and to be growing bigger each second.
