Scientific American

February 1994 Volume 270 Number 2

The Future of American Defense

Philip Morrison, Kosta Tsipis and Jerome Wiesner

As the only superpower in a world of brushfire wars, the U.S. needs armed forces that can be deployed quickly. They must also be reorganized according to mission—a strategy that proved itself during the Gulf War. The trend toward collective security and the absence of a world-class foe mean that the overall size of the armed forces can be sharply reduced, freeing resources for other public needs.

Sulfate Aerosol and Climatic Change

Robert J. Charlson and Tom M. L. Wigley

Compounds of sulfur give the earth's atmosphere a built-in thermostat. They scatter sunlight back into space before it can contribute to global warming. Unhappily, sulfate aerosol complicates the problem rather than solving it. Distribution around the world is uneven, and aerosol has no effect during the night. Eliminating sulfur emissions could greatly accelerate the warming by greenhouse gases.

The Molecular Architects of Body Design

William McGinnis and Michael Kuziora

They are a family of genes, many of which appear in a broad, diverse array of species that ranges from yeast to human beings. Misplaced activity by these genes can turn a healthy embryo into a monster. That phenomenon and the ability to transfer genes between species provide researchers with a powerful way of bringing into sharp focus the process by which genes control development.

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68 D

Science in Pictures

When Is Seeing Believing?

William J. Mitchell

George Bush and Margaret Thatcher nuzzling in a garden? Marilyn Monroe ecstatically taking Abraham Lincoln's arm? Digital manipulation of photographs can produce seemingly incontrovertible evidence of events that never happened.

Liquid Mirrors

Ermanno F. Borra

Great, glass telescope mirrors have enabled astronomers to make breathtaking discoveries. But such tools have real drawbacks. Beyond a certain size, gravity warps them. They are also costly and difficult to manufacture. An alternative is a liquid lens of mercury or gallium. When spun, the metal naturally assumes a parabolic shape. The construction of the vessel and other components is inexpensive.

Scientific American (ISSN 0036-8733), published monthly by Scientific American, Inc., 415 Madison Avenue, New York, N.Y. 10017-1111. Copyright © 1994 by Scientific American, Inc. All rights reserved. No part of this issue may be reproduced by any mechanical, photographic or electronic process, or in the form of a phonographic recording, nor may it be stored in a retrieval system, transmitted or otherwise copied for public or private use without written permission of the publisher. Second-class postage paid at New York, N.Y, and at additional mailing offices. Canada Post International Publications Mail (Canadian Distribution) Sales Agreement No. 242764. Canadian GST No. R 127387652. Subscription rates: one year $36 (outside U.S. and possessions add $11 per year for postage). Subscription inquiries: U.S. and Canada (800) 333-1199; other (515) 247-7631. Postmaster: Send address changes to Scientific American, Box 3187, Harlan, Iowa 51537. Reprints available: write Reprint Department, Scientific American, Inc., 415 Madison Avenue, New York, N.Y. 10017-1111, or fax: (212) 355-0408.

AIDS and the Use of Injected Drugs

Don C. Des Jarlais and Samuel R. Friedman

Hypodermic needles and syringes serve as major vectors for the human immunodeficiency virus (HIV) among drug users. Distribution of clean needles, treatment and education have been found to curb behavior that spreads the deadly virus. Yet, the authors say, public officials have hesitated to implement such programs.

The Terror Birds of South America

Larry G. Marshall

A typical specimen stood almost 10 feet tall, had a massive beak, sported great shredding talons, ran like a racehorse and doted on fresh, raw meat. About 65 million years ago they perched atop the food chain on the emerging continents of the Atlantic Basin. Then mammalian predators dislodged them.

Trends in Physics

Particle Metaphysics

John Horgan, senior writer

Only recently, physicists seemed on the verge of finding a unified theory of all of nature's forces. Yet now they have reached a serious impasse. Even if the Superconducting Super Collider were to be built, it could not achieve the energies at which unification is thought to occur. There is scant hope that low-energy experiments will yield progress. The latest theories do not generate testable predictions.

Master genes Clear need for clot-busters Fertility: the new ethics Bye-bye, greenhouse effect?... More quantum puzzlement Time machines? Cash in your ticket Profile: Bruce M. Alberts, laid-back leader of the National Academy of Sciences.

108 a

108 a

Electrons terrorize newsroom!... Ecocars Is health reform an agent of Big Brother?... Here come the knowbots . . . . Tragedy of the lawns . . . . The Analytical Economist: Does the market always make the best choice? A view from the Chunnel.

DEPARTMENTS

Science and the Citizen

Master genes Clear need for clot-busters Fertility: the new ethics Bye-bye, greenhouse effect?... More quantum puzzlement Time machines? Cash in your ticket Profile: Bruce M. Alberts, laid-back leader of the National Academy of Sciences.

Science and Business

Electrons terrorize newsroom!... Ecocars Is health reform an agent of Big Brother?... Here come the knowbots . . . . Tragedy of the lawns . . . . The Analytical Economist: Does the market always make the best choice? A view from the Chunnel.

Letters to the Editors

Raising the Vasa Questions of power Credit due Fermat.

50 and 100 Years Ago

1894: Public telephones Cholera Rapid transit.

The Amateur Scientist

How to build a telescope mirror by spinning a liquid.

Book Reviews

Eyeing trilobites Nuclear energy Chemical reactions.

Essay: GerardPiel Population growth: development, not AIDS, is the answer.

THE COVER image was created in a computer by blending an 1863 photograph of Abraham Lincoln with a publicity shot of Marilyn Monroe made in 1955. Both images were scanned and then digitally manipulated; a description of the process appears on page 72 of the article "When Is Seeing Believing?" by William J. Mitchell. The ability to transform photographs in this way has brought to an end the 150-year period during which photography seemed unassailable. And it has left us with the task of learning to view photographs with a new wariness.

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