Presently Calhoun looked at the pictures the photorecorder had taken while the telescope's field swept over the city. It was the colony-city reported to have been begun two years before, to receive colonists from Dettra Two. It was the city of the landing grid which had tried to destroy the Med Ship as a dog kills a rat--by shaking it to fragments, some fifty thousand miles in space. It was the city which had made Calhoun land with his vision-plates blinded, that had made him pretend his ship was internally a wreck: which had drained his power-reserves of some hundreds of millions of kilowatt hours of energy. It was the city which had made his return to Med Headquarters impossible. He inspected the telescopic pictures. They were very clear. They showed the city with astonishing detail. There was a lacy pattern of highways, with their medallions of multiple-dwelling units. There were the lavish park areas between the buildings of this planetary capital. There was the landing grid itself--a half-mile-high structure of steel girders, a full mile in diameter. But there were no vehicles on the highways. There were no specks on the crossing bridges to indicate people on foot. There were no copters on the building roofs, nor were there objects in mid-air to tell of air traffic. The city was either deserted or it had never been occupied. But it was absolutely intact. The structures were perfect. There was no indication of past panic or disaster, and even the highways had not been overgrown by vegetation. But it was empty--or else it was dead. But somebody in it had tried very ferociously and with singular effectiveness to try to destroy the Med Ship. Because it was a Med Ship. Calhoun raised his eyebrows and looked at Murgatroyd. "Why is all this?" he asked. "Have you any ideas?" "_Chee!_" shrilled Murgatroyd. II "The purpose of a contemplated human action is always the attainment of a desired subjective experience. But a subjective experience is desired both in terms of intensity, and in terms of duration. For an individual the temptingness of different degrees of intensity-of-experience is readily computed. However, the temptingness of different durations is equally necessary for the computation of the probability of a given individual performing a given action. This modification of desirability by expectable duration depends on the individual's time-sense: its acuity and its accuracy. Measurements of time-sense--" _Probability and Human Conduct_ Fitzgerald