Cover; May 1995; Scientific American Magazine; by Staff Editor; 1 Page(s)

Table of Contents; May 1995; Scientific American Magazine; by Staff Editor; 2 Page(s)

Masthead; May 1995; Scientific American Magazine; by Staff Editor; 1 Page(s)

Letters to the Editors; May 1995; Scientific American Magazine; by Staff Editor; 1 Page(s)

50 and 100 Years Ago; May 1995; Scientific American Magazine; by Staff Editor; 1 Page(s)

MAY 1945 A recent development in plastics and electronics is a wafer-thin Vinylite plastics record, only seven inches in diameter. Each side of the disk will record approximately 15 minutes of dictation. These records can be bent, rolled, dropped, and written on with a pencil without harming the sound track. The thin plastic can be stored indefinitely, without warpage, breakage, or distortion, in an ordinary filing cabinet--100 disks to the inch--and played back at least 100 times.

A new type of Diesel engine will enable the operator to use either gas or oil as fuel without any electrical sparking device and will cut fuel consumption of gas engines by as much as 25 percent. The unit operates on a wide variety of fuels, including fuel oil, natural gas, manufactured and coke oven gases, sewage gas, and refinery by-products. Furthermore, the engine will have the same fuel economy regardless of the type of fuel used.

Information Have-Nots; May 1995; Scientific American Magazine; by Gibbs; 2 Page(s)

Researchers at Addis Ababa University face a disheartening sight when they visit the library to catch up on advances in their fields. Shelves that just six years ago were filled with the latest issues of more than 1,200 academic journals lie barren. The elimination of its foreign currency budget in 1989 forced the library to cancel about 90 percent of its subscriptions, severing the conduit that conveyed news of discovery to scientists in the Ethiopian capital.

Throughout Africa and many other parts of the developing world, the flow of scientific information from the rich countries of the North has dried up over the past decade. The squeeze tightens a vicious circle that dooms many poor nations to waste precious investments in science and technology on duplicative research of dubious quality. Scienti fic American's interviews with more than 40 scientists in 18 countries reveal that many believe poverty, cultural differences and a subtle prejudice against so-called Third World researchers combine to largely shut them out of major journals, important international conferences and critical databases.

The Sound of One Tree Breathing; May 1995; Scientific American Magazine; by Schneider; 1 Page(s)

As part of the Southern Oxidants Study, Environmental Protection Agency researchers and their colleagues at Duke University are conducting experiments to determine the amount of volatile organic compounds (VOCs) given off by some native tree species. Such natural hydrocarbons are of particular concern because they can react with oxides of nitrogen to form lowlevel ozone, a serious atmospheric pollutant.

In order for the EPA to formulate strategies to control levels of hydrocarbons and nitrogen oxides resulting from human activity, researchers must establish the rates at which trees release VOCs. Some studies have suggested that in the U.S., naturally occurring volatile organics might exceed those introduced by cars or manufacturing. But these estimates are highly uncertain, and more direct measurements of biogenic sources are sorely needed. So a few trees must suffer in temporary confinement while their effusions are collected and carefully measured (right ). At least no one is trying to make gasoline this way.

The Cold War's Dirty Secrets; May 1995; Scientific American Magazine; by Beardsley; 1 Page(s)

Over the past year a federal advisory committee has doggedly dragged into public view thousands of government-funded studies in which people were deliberately exposed to radiation. The details, to be released in a report next month, are chilling. Some of the tests--conducted between 1944 and 1974--exposed humans to levels of radioactivity now known to be dangerous, and the number of subjects appears to be far greater than previously realized. It is also coming to light that many patients were not well informed about possible dangers or were deceived outright. Perhaps most distressing of all, the Advisory Committee on Human Radiation Experiments has determined that informed consent was required but ignored.

Some of these horror stories have been known for years. At the top of the list are studies conducted at the University of Rochester and elsewhere in which 18 people were injected with plutonium, 17 of them unknowingly. The tests were designed to determine the risks the substance posed to laboratory workers. Although some of the doses were considered lethal at that time, Wright Langham, then at Los Alamos Scientific Laboratories, justified the work by saying the subjects were hopelessly ill. Nevertheless, four of these "doomed" participants survived another 20 years.

Tribal Struggle; May 1995; Scientific American Magazine; by Mukerjee; 3 Page(s)

Over the 18 square miles of North Sentinel Island in the Bay of Bengal roams possibly the most isolated tribe on the earth. For centuries these 100-odd hunter-gatherers have enforced their seclusion by greeting approaching ships with arrows. Nearby, on other islands of the Andaman chain, related Negrito groups evince different hazards of battling civilization. Some, having lost, are dying of disease and mysterious sterility. Others pursue guerrilla warfare, vanishing into forests after moonlit raids on immigrant villages.

Negrito tribes everywhere are declining, observes Ranjit K. Bhattacharya of the Anthropological Survey of India. Soon these remnants of a people who once ranged across Southeast Asia may be gone as well. But not without a fight.

Sponging off Shrimp; May 1995; Scientific American Magazine; by Vames; 1 Page(s)

Sponges are not picky eaters: they dine on nearby particles or microorganisms. But the discovery of flesh-eating sponges in a Mediterranean cave suggests that the phylum Porifera may be more diverse--and perhaps more discerning--than scientists thought. The sponges, from the family Cladorhizidae, were found by Jean Vacelet and Nicole Boury-Esnault of the University of Aix- Marseilles II. They resemble sponges known to exist only in ocean depths.

Finding these creatures in shallower waters enabled the researchers to document their feeding process. Prey are held by filaments covered in small, hookshaped spicules, which act like Velcro (left ). Epithelial cells on the outer surface gradually migrate toward the captured food, in this case a shrimp, and envelop it (micrograph at right ). Once absorbed, the meal is digested over the course of a few days, and new filaments grow in the place of old ones.

Top Price for the Top Quark; May 1995; Scientific American Magazine; by Horgan; 2 Page(s)

After years of rumored sightings, researchers at Fermilab in Batavia, Ill., finally, officially, found the fat but fleeting top quark--one of a class that combines to form neutrons and protons--this past March. Although most physicists considered the result a foregone conclusion, the New York Times saw fit to announce it on page one; in the story, Energy Secretary Hazel R. O'Leary called the finding a "major contribution to human understanding of the fundamentals of the universe."

O'Leary is hardly a neutral observer, since the Energy Department is the biggest supporter of U.S. particle physics. Rustum Roy, a materials scientist at Pennsylvania State University and a critic (to put it mildly) of particle physics, has a different perspective. The short version of his response to the news was: "Who gives a damn?" Roy charges that such findings do not justify their cost. Particle physics will receive $642 million this year from the Energy Department and $57.6 million from the National Science Foundation; Fermilab consumed more than $1 billion in the seven years it spent tracking down the top quark.

Why Worry?; May 1995; Scientific American Magazine; by Stix; 2 Page(s)

We are all going to die. The likelihood of how and when becomes quickly muddled by the latest statistics on traffic deaths or on the risks of getting cancer from consuming a peanut butter sandwich every day. Because this barrage of information creates such confusion, John Paling, a former biology professor at the University of Oxford, came up with what he describes as a Richter scale to gauge the dangers of daily living. He got the idea after observing a woman smoking a cigarette while inquiring about the benefits of buying a water-purification kit.

Paling describes his scale in Up to Your Armpits in Alligators? How to Sort Out What Risks Are Worth Worrying About. Risks are identified with negative and positive numbers. The midpoint, 0, represents a one-in-a-million hazard, the point below which the cancer risk from a food additive is too small to be of concern to the Food and Drug Administration. Between -2 and -4 are one-of- a-kind risks, the chance of something happening once a year in the entire U. S., what Paling calls the "Bobbitt zone." Going up the scale are still rare threats such as drowning in a bathtub. Above +2, anxiety starts to rise; +6 represents a million-in-a-million risk--in other words, our days are numbered.

So Many Salmon, But So Little; May 1995; Scientific American Magazine; by Zorpette; 2 Page(s)

The annual return of salmon to the streams of their birth is one of nature's great pageants and a dramatic prologue to the spectacle of seasonal change near the rugged edges of the earth's temperate zones. In the Northern Hemisphere, however, evidence of fundamental changes in this ancient ritual has begun to accumulate.

For more than 20 years, various studies on Pacific Rim rivers have noted that the size of this fish, prized by anglers and epicures alike, has declined. In a study presented last October, biologists Brian Bigler and John H. Helle made the first thorough assessment of the problem: reduced sizes are being found throughout the North Pacific, in a vast area stretching from Japan to California. "It is astonishing and frightening," says Bigler of Wards Cove Packing Company, a commercial fishing concern.

Life's a Draw; May 1995; Scientific American Magazine; by Beardsley; 2 Page(s)

Arguments over the role of chance events in evolution have long divided biologists. One camp emphasizes the awesome power of natural selection to shape biological forms. Another group, whose most prominent member is Stephen Jay Gould of Harvard University, points out that random happenings--a drought here, an earthquake there--also play a key part.

In principle, the role of chance could be determined by rerunning evolution. If it took much the same course the second time around, that would support the selectionist camp. If replaying life's tape generated an entirely different biota, it would indicate the importance of random events.

The Naughtiest Teens in the World; May 1995; Scientific American Magazine; by Gibbs; 1 Page(s)

Surprise: it is not America¿s youth. The first study using nearly identical survey methods to measure adolescent delinquency rates in five European nations and nine Western cities found that Athenian juveniles rank highest. Americans should not gloat, however: young Nebraskans led the world in violent attacks.

As They Lay Dying; May 1995; Scientific American Magazine; by Yam; 2 Page(s)

Not too many personal computers are known to hallucinate. But the one belonging to Steven Thaler has been doing so, off and on, for the past couple of years. The physicist, at McDonnell Douglas in St. Louis, has been exploring what happens as an artificial neural network breaks down. But rather than allowing the network to peter out into oblivion, Thaler has a second network observe the last gasps of its dying sibling. Some of those near-death experiences, it turns out, are novel solutions to the problem the net was designed to solve. Thaler says he has found a kind of creativity machine that can function more quickly and efficiently than traditional computer programs can.

An artificial neural network is software written to mimic the function and organization of biological neurons. The system consists of units (representing neurons) connected by links (standing in for dendrites and axons). Like the brain, an artificial network can learn: the programmer presents it with training patterns, which it learns by adjusting the strengths, or weights, of the links. Many researchers use these networks to model brain function and, by destroying part of the net, to mimic disorders such as dyslexia.

The Analytical Economist; May 1995; Scientific American Magazine; by Stix, Wallich; 2 Page(s)

In 1960 South Korea's gross domestic product per capita was lower than that of many sub-Saharan countries. During the next 30 years, South Koreans saw this measure of national output jump by an average of nearly 7 percent annually as they rocketed past once far wealthier Brazilians and Argentines. Other East Asian countries also tallied extraordinary growth statistics. Korea, Hong Kong, Taiwan and Singapore became collectively known as the Four Tigers, the Four Dragons or, with an occasional touch of derision or envy, the Gang of Four. Other members of this fast-track club include Japan, Malaysia, Indonesia and Thailand.

Economists, sociologists and political scientists have made careers out of studying the ingredients that shaped the region's economic accomplishments. Books, papers and doctoral theses have weighed in on the lessons that could be gleaned for a Paraguay or a Chad, countries that have yet to achieve an economic takeoff. But no final consensus has been reached on the secrets of success.

Lithography Becomes Political Pork; May 1995; Scientific American Magazine; by Stix; 1 Page(s)

The Superconducting Super Collider is dead, but legislators with a taste for high-tech pork can still pig out on lithography. Like particle physics, lithography--the technique for making circuit patterns on microchips-- requires focused beams of energy and large infusions of cash.

More than half of the nearly $60 million in the Department of Defense's main lithography program for the 1995 federal budget was targeted by Congress for pet projects--including the use of x-rays or short wavelengths of ultraviolet light to create a circuit pattern on a chip. Legislators either specified an amount or asked the department 's Advanced Research Projects Agency (ARPA) to decide how much the designated research should receive. Either way, lawmakers who would have difficulty distinguishing a memory chip from a microprocessor have usurped at least some of the job responsibilities of ARPA's engineering wizards.

A Rogue's Routing; May 1995; Scientific American Magazine; by Wallich; 1 Page(s)

The technique that hacker Kevin Mitnick used to break into a computer- security expert's machine (and onto the front page) was published almost 10 years ago by Cornell University graduate student Robert Morris-- the father of the worm that shut down the Internet briefly in 1988--during his summer stint at AT&T Bell Laboratories. No one had used it before, says Bell Labs computer scientist Steven M. Bellovin, because there were so many easier ways of cracking most systems.

Bellovin and others have worked out a modification to Internet protocols that would prevent Mitnick's technique from working again. But malicious hackers have had a decade's worth of technical literature to draw on since then.

Feature from the Dark Lagoon; May 1995; Scientific American Magazine; by Schneider; 1 Page(s)

Peering at shipwrecks in murky depths has been, until recently, a dim affair. But a new development in underwater sensing, the laser line scanner, is clearing things up. Normally, underwater imagery is hampered by the abundance of suspended particles that scatter light like dense fog--as in this video frame of a submerged World War II torpedo bomber (left). This limitation restricts subsurface photography to close-up views and makes it difficult to capture large objects.

The new system circumvents that problem, yielding sharp images of, for instance, the same bomber (right). The optical instrument uses a single blue-green laser to scan the subject, one line at a time, much like the electron beam of a television picture tube. Blue-green light penetrates seawater more effectively than do other colors, and because the illumination is focused in a single narrow swath, it does not scatter back from all directions as would light from conventional sources.

Putting the Mass Back in Transit; May 1995; Scientific American Magazine; by Stix; 2 Page(s)

The empty seats of the automobiles that U.S. commuters drive every day could hold nearly all 250 million Americans. This calculation is testament to the growth of the suburbs and the failure of public transportation to provide access to the vast tracts of housing that extend almost 100 miles away from urban centers.

A few pioneers are now trying to use computer and communications technologies to broaden the definition of mass transit to encompass everything except a car with only a driver. The work of these innovators is hidden away as a small piece of the hundreds of millions of dollars in annual federal and state research and development spending that goes by the name Intelligent Transportation Systems (ITS). The ITS has been investigating how drivers could use radar to detect hard-to-see objects on the road or even relinquish control of a car to a remote computer.

Electric Genes; May 1995; Scientific American Magazine; by Paterson; 2 Page(s)

As more and more of the human genetic blueprint is unraveled, the pressure to know what it means for people grows. Does the baby have any serious genetic problems? Does that teenager carry genes predisposing her to breast cancer? Does a particular adult have the DNA associated with diabetes or with Alzheimer's disease?

During the past few years, it has become possible to provide answers to more of these questions--to find, for example, the Apo E4 gene that indicates a greater risk of Alzheimer's or the BRCA1 gene associated with certain cases of breast cancer. But at present such testing is limited to patients in research projects or those who have a family history of the disease. Widespread speculative genetic screening of populations is too costly to consider--even were it ethically acceptable. This situation may be about to change, at least from a technical standpoint.

Europeans On-Line; May 1995; Scientific American Magazine; by Browning; 1 Page(s)

Wiring Europe is providing the first real test of one of the more optimistic assumptions of cyberspace: there are no limits in the electronic realm, because national borders can be vaulted with a flick of the mouse. True, technology can render such boundaries meaningless, but do people want that to happen? The answer will determine the fortunes of the companies rushing to hook up Europe.

At first glance, Europe is ripe for the wiring. Although it has a slightly larger population than does the U.S. (where seven million Americans cavort in cyberspace), only a few hundred thousand Europeans have found an on-ramp to the information superhighway. Sales of personal computers and modems are rising; in Britain some 4,000 households sign on to the Internet every month. Nevertheless, corporations vying for Europe's attention may be in for a rude shock. Europeans long ago learned to cope with differing national preferences in everything from cheese to washing machines. But on-line services are new territory, dominated by Americans, who have not (yet) had to worry about internationalization.

Profile: Brian D. Josephson; May 1995; Scientific American Magazine; by Horgan; 2 Page(s)

Brian D. Josephson, Nobel laureate, stands at an incandescent intersection in Tucson, Ariz., squinting through thick black spectacles, lost. His floppy white hat has been pulled down so far that--intentionally?--it almost conceals his dark-browed, furtive face. He wears a black T-shirt bearing the digitized likeness of Alan S. Turing, another British prodigy whose relations with the scientific establishment were troubled.

So, let's see, Josephson mutters, as traffic roars and squeals around him. Someone at the meeting Josephson is attending here has recommended a "very good" restaurant within a few blocks of the conference center, but he's not sure exactly where it is. We cross the street, wander some more, and finally Josephson exults, "Ah, that's it."

The Global Tobacco Epidemic; May 1995; Scientific American Magazine; by Bartecchi, MacKenzie, Schrier; sidebar by Pierce & Gilpin; 8 Page(s)

Since the early 1960s, medical research, public information campaigns and government assessments have exposed the dangers of tobacco smoke. The result has been a substantial drop in the number of smokers in the U.S.--from a peak of 41 percent to its current level of about 25 percent. Yet despite considerable scienti fic evidence and continuing exhortations from the medical community, the trend has now mostly ceased: the number of adult smokers has remained static since 1990. Similarly, the proportion of adolescents who smoke has changed little in the past 10 years. Perhaps even more disconcerting is that in the global picture, cigarette production during the past two decades has increased an average of 2.2 percent each year, outpacing the annual world population growth of 1.7 percent. Because of growing cigarette consumption in developing nations, worldwide cigarette production is projected to escalate by 2.9 percent a year in the 1990s, with China leading the way with jumps near 11 percent a year.

To understand the driving forces behind modern directions in tobacco consumption and to formulate strategies to combat its pervasiveness, the medical community has had to extend observations beyond the individual smoker and the addictive power of nicotine. The focus of some recent work has been on the tobacco industry itself. In this context, changes in smoking behavior depend in large part on cigarette pricing, advertising, promotion and exportation. Researchers in preventive medicine and public health agree that education campaigns must be supplemented. The new strategies should aim to regulate the marketing of cigarettes, to raise taxes on tobacco and to rethink current trade practices

Binary Neutron Stars; May 1995; Scientific American Magazine; by Piran; 8 Page(s)

In 1967 Jocelyn Bell and Antony Hewish found the first pulsar. Their radio telescope brought in signals from a source that emitted very regular pulses every 1.34 seconds. After eliminating terrestrial sources and provisionally discarding the notion that these signals might come from extraterrestrial intelligent beings, they were baffled. It was Thomas Gold of Cornell University who realized that the pulses originated from a rotating neutron star, beaming radio waves into space like a lighthouse. Researchers soon tuned in other pulsars.

Even as Bell and Hewish were making their discovery, military satellites orbiting the earth were detecting the signature of even more exotic signals: powerful gamma-ray bursts from outer space. The gamma rays triggered detectors intended to monitor illicit nuclear tests, but it was not until six years later that the observations were made public; even then, another 20 years passed before the bursts' origin was understood. Many people now think gamma-ray bursts are emitted by twin neutron stars in the throes of coalescence.

Dendrimer Molecules; May 1995; Scientific American Magazine; by Tomalia; 5 Page(s)

In the center of Michigan, along the Chippewa River, some 130 miles southeast of Sleeping Bear Dunes National Lakeshore, the land is not productive enough for traditional agriculture, but it is adequate for growing trees. Thousands of trees of all types, with every branching pattern and shape imaginable, flourish there. Year after year young seedlings with single trunks emerge. Then their trunks elaborate branches, and those branches produce more branches in the same way, giving rise to the lush and varied forest.

As I pondered these trees near my home some 20 years ago with the eyes of a chemist, the systems of branches made me wonder whether one could design large, precisely defined molecules by adding branch after branch onto some original substance. The idea of gaining such control over the formation of a molecule appealed to me immediately on both theoretical and practical grounds, but it was not until the end of the 1970s that I found a way to put the concept into practice. Today my technique and other similar approaches are making it possible to construct treelike molecules that mimic a variety of biological structures, including proteins. There is good reason to believe that these synthetic constructions will prove valuable in medicine, the electronics industry and other fields.

The Ocean's Salt Fingers; May 1995; Scientific American Magazine; by Schmitt Jr.; 6 Page(s)

In the mid-1950s Henry M. Stommel and Arnold B. Arons, researchers at the Woods Hole Oceanographic Institution, stood staring at a chalkboard, groping for a way to measure the pressure at the bottom of the sea. In desperation they were considering constructing a three-mile-long tube from the surface to the bottom and drawing the ocean's deepest water up into the pipe. Because water is less salty near the seafloor than at the surface, the column of water within the tube would, after coming to thermal equilibrium, be lighter and so stand higher than the ocean surface around it.

Stommel and Arons imagined that they could then easily measure changes in pressure at the base of this ungainly instrument by watching the water level in the tube go up and down. As they gazed at their sketch, focused entirely on the problem of pressure measurement, Arons suddenly got a strange idea. He added a spigot to the top of the pipe in the diagram and said, "Hank, if we open the faucet, it will run forever." Stommel dubbed this astonishing mental construction "the perpetual salt fountain." He and his colleagues immediately convinced themselves of the veracity of their idea by setting up a model salt fountain in the laboratory. Subsequently, they attempted to fabricate an actual salt fountain at sea, although their modest efforts toward a full-scale demonstration of the concept gave ambiguous results.

The Silicon Microstrip Detector; May 1995; Scientific American Magazine; by Litke, Schwarz; 6 Page(s)

Silicon, the elixir of the electronics revolution, has long been known as a material of uncommon adaptability. Now, roughly half a century after the discoveries that eventually ushered in today's world of ubiquitous computers, communications technologies and photovoltaic cells, this versatility appears headed toward remarkable heights. Coming years promise chips that will let electronics communicate with human nerves and tiny machines able to perform microsurgical tasks.

Yet another fascinating application is in detecting charged particles, in which a kind of silicon-based microscope is used to peer into the very heart of matter. Fifteen years in the making, the silicon microstrip detector allows physicists to measure the positions of particles to within 10 microns or less. Such precision--at least 10 times better than what has been readily achievable with previous electronic particle-detection technologies--has opened new experimental possibilities in particle physics and other scientific fields.

The Atomic Intrigues of Niels Bohr; May 1995; Scientific American Magazine; by Staff Editor; 1 Page(s)

Scandal is not usually linked with the name Niels Bohr; genius and character are. The Nobel Prize¿winning physicist who first described the atom through quantum mechanics was a titan of 20th-century science. During World War II, he opposed the Nazi occupation of his native Denmark and as a refugee participated in the Manhattan Project, which gave nuclear might to the U.S. Yet Bohr was also an outspoken advocate of international cooperation, urging Franklin D. Roosevelt and Winston Churchill to provide other countries with knowledge of the bomb's workings in the interest of world peace.

Would Bohr have acted unilaterally on those convictions? Last year some seemingly wellplaced sources publicly alleged that Bohr had given classified information about the U.S. bomb program to Soviet agents. Suspicions centered on a meeting between Bohr and representatives of the secret police that took place in 1945.

Did Bohr Share Nuclear Secrets?; May 1995; Scientific American Magazine; by Bethe, Gottfried, Sagdeev; 7 Page(s)

This sensational allegation from the 1994 book Special Tasks goes on to accuse Niels Bohr, as well as other famous Manhattan Project scientists, of providing Soviet spies with confidential information about the American effort to develop nuclear bombs. The book, based on the recollections of Pavel Sudoplatov, one of Joseph Stalin's most senior secret police officers, does not document its grave charges with any evidence. Nevertheless, the book's publication triggered an intense controversy about the truth of the claims.

Recently a memorandum to Stalin that describes the contact with Bohr was released from the KGB archives. The document contains a supposedly verbatim transcript of the very meeting, held in November 1945, in which Bohr allegedly supplied the Soviets with classified information. We have now reviewed this document thoroughly and find it is evidence that the charges against Bohr are false.

What Did Heisenberg Tell Bohr about the Bomb?; May 1995; Scientific American Magazine; by Bernstein; 6 Page(s)

In September 1943 Niels Bohr learned that the gestapo in Copenhagen intended to arrest him. A few weeks later, on the 29th, he, his wife and several others hoping to escape from Denmark crawled in complete darkness to a beach outside Carlsberg. There they boarded a boat and crossed the ¿resund in secret to Sweden. On October 6 the British flew Bohr alone from Sweden to Scotland. Later that same day he traveled to London and in the evening met with Sir John Anderson, the physical chemist in charge of the nascent British atomic bomb project. Anderson gave the Danish physicist a briefing on the Anglo-American program. According to Bohr's son Aage, who followed his father to England a week later and was his assistant throughout the war, Bohr was deeply surprised--shocked may be a better description--by how far the Anglo-American program had already progressed.

Bohr's alarm very likely had two sources. First, during the 1930s, when nuclear physics was developing, Bohr had said on several occasions that he thought any practical use of nuclear energy was all but impossible. That view was reinforced in the spring of 1939, when he realized an important detail concerning the fission of uranium. In December 1938 the German physical chemists Otto Hahn and Fritz Strassmann had discovered that uranium could be fissioned if it was bombarded with neutrons. (Hahn's former assistant Lise Meitner and her nephew Otto Frisch conjectured that the uranium nucleus had actually been split in the experiments and so coined the name "fission" for the process.) The experiments used natural uranium, 99 percent of which is in the isotope uranium 238. About seven tenths of a percent is in the isotope uranium 235, whose nucleus contains three fewer neutrons.

The Preservation of Past; May 1995; Scientific American Magazine; by Holloway; 8 Page(s)

Just before sunset, the stones of Pueblo Bonito in Chaco Canyon, New Mexico, glow golden, and their varied patterns stand out like friezes. The ruin--an elaborate city built and inhabited by Anasazi Indians between A.D. 850 and 1150--becomes empty of the day's tourists, and the cold of the desert night begins to settle in the shadowy rooms and Kivas, circular ceremonial centers sunken in the ground. The small vents and tapered doors grow black.

One of these dark entrances--a high, squat door sitting at the junction of two walls--captures the attention of Dabney Ford, an archaeologist with the National Park Service who has worked at and studied Chaco Canyon for more than 10 years. She explains that the opening is aligned to catch sunlight only on the winter solstice. On that day, rays of light reflect on a specially built wall corner on the opposite side of the room. Although archaeologists understand relatively little about Anasazi culture, some have recently come to believe that the design of Pueblo Bonito--like that of Teotihuac.n in Mexico, Machu Picchu in Peru and many other ancient cities--reflects astronomical cycles. The door is just one example of an architecture oriented by solar and lunar fluxes-- one that perhaps embodies Anasazi political and social hierarchy.

Mathematical Recreations; May 1995; Scientific American Magazine; by Stewart; 3 Page(s)

Atoast, ladies and gentlemen: To the Queen!" We stood, dutifully raised our glasses and murmured the sovereign's name. It should have been a poignant moment, but it was spoiled by the person next to me, who flopped back into his chair and muttered, "Thank God, now I can smoke!" (It is a quaint British custom that at a formal dinner no one may smoke before the party drinks to the queen's health.)

I'd rather you didn't, I said. "I'm a nonsmoker." "You had the smoked salmon," he said and roared with laughter as he lit a cigarette. I wrinkled my nose and glanced at his badge: Richard Byrd. He had penciled in, "Call me Dicky."

Book Reviews; May 1995; Scientific American Magazine; by Morrison, Davis; 5 Page(s)

This book opens with a generous gift to us all. It was made early in 1990, when the space probe Voyager completed its scripted dozen-year tour of duty. Well beyond Neptune and far north of the plane of the solar system, the craft received a final set of new commands, no part of the original mission. Look back, Voyager, to the now distant inner planets! Carl Sagan and a few others had argued and waited years for the Jet Propulsion Laboratory and NASA to schedule a shoestring effort to snap just one candid portrait of the earth among the planets. They succeeded brilliantly.

The spacecraft recorded a mosaic of 60 frames, planets against the sky. It sent the bits to far-off earth; that slow video transmission from past its design range took three months. The four planets in clear view would at best be mere dots of light. (The glare of the sun only six light-hours away from the camera masked nearby Mercury. Pluto and Mars happened to be poorly placed. Uranus and Neptune were so faint that they required long exposure; they could not help themselves from moving, so their images are streaked.) Our earth entire is seen as one bright bluish dot in the image that faces the title page.

Essay; May 1995; Scientific American Magazine; by Mitchell; 1 Page(s)

This nerdy variant on the old Halloween joke about the skeleton neatly encapsulates some commonly expressed hopes and flip-side fears about the Information Superhighway--that it will inexorably replace transportation with telecommunication, face-to-face meetings with transactions in cyberspace and human secretaries and assistants with disembodied software agents. In reality, a robust infobahn is likely to produce a considerably more complex and subtle redistribution of functions among buildings, transportation systems and computer networks. Let me illustrate this point with a homely story I call "The Parable of the Pizza Parlor."

Not so long ago pizza parlors were mostly found on Main Street. They had advertising signs out front to pull in customers, counters where those customers placed orders and handed over cash, kitchens where pizza was baked and an eating space containing tables and seats. All these components were wrapped up in one small building.