“The explanation was quite simple. The hot day had warmed the air close to the pavement, but the cooling of the surface at the onset of darkness had caused a layer of warm air to be sandwiched in between the cold air close to the road surface and the cold air above. This acted like a lens which produced an out-of-focus image of a bright tavern sign more than fifty miles away, a real mirage. There were few cars on the road, but as we met them the effect was most startling because some of them were so enlarged by the lens effect that a car five miles away seemed to be rushing directly at us only a block or two ahead. Sometimes these cars would appear to come to a sharp stop, reverse their course and disappear in the distance. At other times they would appear to be rushing on us upside down, with part of the road itself in the sky. Altogether it was a weird experience, but not in any sense supernatural. Lenses of air, either close to the ground or in the sky, can produce strange illusions.” In this case, as in many UFO puzzles, the solution depended on a knowledge of the weather conditions and of the facts of local geography. If the pursuing car had turned off the road or stopped for the night before reaching the tavern, the specific cause of the phenomenon might still be a mystery. _The Chesapeake Bay Case_ Two of the most famous UFO cases, the Nash-Fortenberry and the Tombaugh sightings, have never been completely explained even though the witnesses were unusually competent, the incidents fully described, and the basic facts not in dispute. Although the probable type of mechanism involved is clear in each case, determining specifically what factors combined in exactly what way to produce the phenomenon has so far proved impossible. Neither case, however, supports the theory that the UFO had an extraterrestrial origin. On the evening of July 14, 1952, a Pan-American DC-4 was flying from New York to Miami, carrying ten passengers and a crew of three including First Officer William B. Nash and Second Officer William H. Fortenberry. As a pilot spending much of his life in the air, Captain Nash had long been interested in the question of UFOs, and during the long night hours of over-water flights he had often cut down the cockpit lights to search the sky. In five years of watching he had observed hundreds of meteors, various types of auroral display, the lights of other aircraft, and the multicolored images of stars and planets distorted by refraction, but he had never seen any unidentifiable aerial phenomenon that appeared to be under intelligent control--until this particular night, when he was not watching for UFOs.