National Geographic : 1989 Feb
ATA NAL G AD AE APHA C end to the effort of Willard Andre Hutt, who was 17 when he first began working on the project. The trail in cludes what the National Park Service calls "magnet sites" that illustrate black history from slavery through the New Deal. Among them are black cemeteries that date from the early 19th century, the first African Method ist Episcopal church in Washington, and the homes of black educator and political activist Mary McLeod Bethune and abolitionist leader and writer Frederick Douglass. Hutt (below), seen in the Douglass home, chose the sites and spent years working with local and national offi cials to get the trail approved. He now is a salesman in Minneapolis. Today there are nearly 800 national recreation trails established under a 1968 law that authorized the National Trails System. CINDYYAMANAKA Aid for Computer-based Geographic Research Academic geographers have turned to computers to help them do their L jobs better and in new and differ ent ways. But the use of computers to improve the understanding of geo graphic data is far from perfect. So the National Science Foundation has awarded a five-year, 5.5-million-dollar grant to a consortium of three universi ties to create a National Center for Geographic Information and Analysis. The consortium-whose members are the University of California at San ta Barbara, the University of Maine at Orono, and the State University of New York at Buffalo-will carry out research aimed at making better use of the mountains of data accumulated in geographic information systems (GIS) by geographers and by society in general. For example, the center will develop programs for many applica tions, such as aiding population evacu ation in a disaster, using electronic maps to show changes as time passes, and giving geographers better access to the ever growing, ever changing infor mation stored in a GIS. The center will also deal with the problem of creating errors while using computers to produce maps. As one geographer noted in a letter to an official of the National Science Foun dation, "We can now produce rubbish faster and with more elegance than ever before." Wishbone in Action: A Real Flexible Flier Anyone who has ever tried to pull apart a wishbone knows that it is AL flexible. X-ray movies of star lings in flight in a wind tunnel show, however, that a wishbone is far more flexible than we have imagined. "We thought that the wishbone might be a strut to stabilize the bird's shoulder while the wings beat," says Farish A. Jenkins, Jr., of Harvard University, one member of the team that revealed the skeleton of a bird in flight for the first time. "What we dis covered instead was that on the wings' downstroke, this V-shaped bone is bent out, and on the upstroke, like a spring, it recoils to its original position." The amount of movement is "extraordinary," says Jenkins. The ends of the wishbone are about 12 milli meters apart when a wingbeat begins (diagram, below) but separate to as much as 18 to 20 millime ters, making the wishbone one of the most dynamic bones in the vertebrate world. And it must be strong enough to take a lot of bending. Typically a star ling flaps its wings 12 to 16 times a sec ond during flight. Jenkins speculates that the wish bone's unusual flexibility helps the bird to breathe in flight. Its movement forces air in and out of the air sacs locat ed between the bone's two shafts. Joining Jenkins in the study were Kenneth P. Dial of the University of Montana and G. E . Goslow, Jr., of Northern Arizona University. NGS PHOTOGRAPHERVICTORR. BOSWELL,JR. Using Science to Date an Icon of Faith n improved method of radiocarbon dating was the key to the dis covery that the Shroud of Turin (GEOGRAPHIC, June 1980) dates from medieval times and could not be Christ's burial cloth. The new method is faster and requires smaller samples of material than older techniques. Carbon dating relies on the fact that carbon dioxide in the atmosphere con tains stable carbon 12 and carbon 13 and a small amount of radioactive car bon 14. All living things continually absorb carbon dioxide, and the ratio of the carbons remains in balance until death. Then radioactive decay reduces the ratio of C 14 toC 12 at a known rate. Half the C 14 disappears in 5,730 years. By measuring the ratio in a piece of wood, cloth, or bone, scientists can determine its age. Three laboratories received a snippet of linen from the shroud. Each was thorough ly cleaned and burned to LASZLOMESZOLY,HARVARDUNIVERSITY produce carbon dioxide and then pure carbon, whose atoms were electrified. A high-energy mass spectrometer sep arated the carbon isotopes and counted their atoms. From their ratio came the fabric's age: The 14-foot linen strip was woven from flax harvested in the late 13th or early 14th century. Scientists have found no evidence of paint, dye, or ink on the shroud. How did it get its faint, realistic image of a crucified man? That mystery radio carbon dating cannot solve.