Produced by Greg Weeks, Stephen Blundell and the Online Distributed Proofreading Team at http://www.pgdp.net _Psychopathology has offered possible answers to why, from time to time, people in large quantities "see" strange things in the sky which manage to evade trained scientific observers, or conform to what is known about the behavior of falling or flying bodies. And mass hysteria is by no means a product of the present century. But--what if these human foibles were deliberately being exploited?_ THE FOURTH INVASION by Henry Josephs Dr. Clayton's face was impassive as a marble mask when he turned to young Corelli. For a moment, the little group stood there in embarrassed silence in the classroom, shifting uneasily from one foot to the other, feigning interest in the paperweights upon Clayton's desk, or in the utterly uninspiring scenes on the sidewalk outside the window. "You say, Corelli, that you saw three--er, Martian--ships. Can you describe them?" Corelli blinked as he felt the weight of his colleagues' eyes boring into him. "I didn't say they were _Martian_, sir--only that they seemed to be unearthly. And they were not the conventional saucer-shaped things--they _acted_ like saucers skimming across the water. That's what made me think they were genuine. And they didn't seem to be going fast enough so that I'd expect to hear a roar like a jet-plane. "It struck me that this might not be the way they fly, naturally, but the way they might fly if the pilots were having trouble adjusting the controls to a heavier atmosphere than they were used to." Clayton tapped the tabletop with his fingers. "What about you, Marty? Did you see three ships?" Big Gene Marty, football star, was the least nervous. "Can't be sure about _ships_, Doc," he rumbled. "I did see something strange disappearing over the horizon. It--I mean they--might have been what Tony says; but whatever it was, there were three of them. But I saw something else, because I was looking in another direction. What I saw first was a couple of funny-looking shapes floating down near the ground. Didn't look like parachutists, yet they seemed big enough to be men--or at least, small men." "Interesting. All right, what about the rest of you? How many saw the ships?" * * * * * A chorus answered him. "I see," Clayton mused. "You all agree on the behavior. And you all think there were three--not four--not two. Three?" It was agreed. Clayton rustled the pile of newspapers. "The reports in here vary. I learn with amazement that you gentlemen seem to have missed completely the spurts of flame that issued from the alien ships--flame which is reported to have set a house on fire. And no one seems to have noticed that the invaders, in descending, glided on huge black wings."