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the right amount ofmoisture in the air, instead offorming tiny droplets, die cold produces a multitude of litde wafer-like crystals. They are disposed in the air as leaves would be or as red cells are in suspension, slowly floating down like leaves. These tiny six-sided plates, all floating more or less flat, catch the light from the sun, bend it at a predictable angle, and condense and concentrate it on the right and left. Greenler has programmed computers to study various mechanisms of such phenomena, including a series of remarkable studies of the effect of odier crystals that are like long six-sided pencils. For decades I have tried to teach students the simplest way of understanding die sedimentation of red cells and what makes it rapid. I had the idea diat, like die lévitation of a Frisbee, individual red cells, in a mainly horizontal arrangement, slip and slide slowly down. When they are stacked up like a long roll of coins, die relationship of surface to weight changes. Instead of being mostly surface, they now have an appreciable volume. I had assumed that in this shape diey would point down and, dius, fall speedily. The pencil-like ice crystals float as a log would, with die long dimension more or less horizontal. But they fall much faster than single cells. Thus, die clearer understanding of sun dogs may make die simple problems of the sedimentation of red cells more comprehensible. Greenler has used computers to study a large array of sights that only an extremely dedicated viewer of natural light phenomena would notice. Among the remarkable discussions are those which not only clarify rainbows, halos, arches, and spots, light pillars, circles, crosses, and complex displays, but tilings that people are more familiar with, such as the aurora borealis. We learned about complex displays, circles, crosses, scattering of light in clouds, the corona, the glory, and the Specter of Brocken. The Specter of Brocken is a remarkable shadow enclosed in a halo cast by a person in the mountains usually soon after the sun has risen as one climbs up into misty sunlight. It moves with the observer—a ghostly shadow named for Brocken, the highest of the Harz Mountains in central Germany—but may be seen in any mountainous region under appropriate circumstances. Mirages, twinkling of stars, the green flash, and other matters of refraction and visual capacity are discussed in great length. The many colored plates, the black-and-white photographs, and the line diagrams and designs, as well as the computer statistics, give one a new and vivid understanding of many of die spectacles of nature uiat can be seen by merely being at the right place, opening one's eyes, and looking. But what the book does, too, is to show how an understanding of nature and its glories can increase our enjoyment of nature. William B. Bean Department ofMedicine University ofIowa, Iowa City The Poisoning ofMichigan. ByJoyce Egginton. New York: W. W. Norton & Co., 1980. Pp. 351. $13.95. The Poisoning ofMichigan is a detailed report of an unusual accident and the inadequate response of government officials and the officers of the commercial Perspectives in Biology and Medicine, 26, 1 · Autumn 1982 | 165 firms concerned. Written by a skillful investigative reporter, it is a combination of suspense story and how-not-to-do-it manual. The point of view is that of the contemporary concerned citizen and the environmentalist. Scientific aspects of the problem receive much less attention dian they deserve, and by 1980, when the book was published, a great deal more information was available which is not mentioned. The title suggests that the incident was considerably more serious than it appears to have been. "Contamination" would be a more appropriate term than "poisoning." Briefly, in the early fall of 1973, a toxic fire-retardant chemical instead of magnesium oxide was added by mistake to a special supplement for dairy cattle prepared by a feed mill operated by Farm Bureau Services, Inc., in Battle Creek, Michigan. No one is quite sure how many farms received the original batch of contaminated feed, but one dairyman, Rick Halbert, received the most. Since the mistake...

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