Hovering like a giant's smoke ring, a great cloud appeared at sunset over Flagstaff, Ariz, last Feb. 28 and set off a continuing scientific mystery. Watchers struck by the cloud's odd shape and huge size, took pictures, like these four, at different times and from widely scattered locations in the state. 

Dr. James McDonald, a meteorologist at the Institute of Atmospheric Physics in Tucson, has been accumulating the pictures. Using them as the basis for trigonometric calculation, he has made a startling discovery that the cloud was at least 26 miles high and 30 miles across - "a lot higher and bigger," he says, "than a cloud should be." 

The circle was too high to be made by a jet plane, and so far as Dr. McDonald can determine, there were no rockets, rocket planes or bombs being tested nearby that day. He hopes anyone else with pictures will lend them to him, for he would like some more clues about the cloud 26 miles up - no water droplets exist at that height to make a cloud. 

The photographs below were scanned from p.112 of Life magazine May 17, 1963.