Cover; September 1999; Scientific American Magazine; by Staff Editor; 1 Page(s)

Table of Contents; September 1999; Scientific American Magazine; by Staff Editor; 2 Page(s)

From the Editors, including Masthead; September 1999; Scientific American Magazine; by Rennie; 1 Page(s)

Letters to the Editors; September 1999; Scientific American Magazine; by Staff Editor; 2 Page(s)

50, 100 and 150 Years Ago; September 1999; Scientific American Magazine; by Staff Editor; 1 Page(s)

TELEVISION AND THE FAMILY-"In nearly two million U. S. homes, the flickering screen of the television set has paralyzed the family in its chairs. Obviously it is about time somebody began to measure the impact of this new social force. Preliminary data from a study sponsored by the Columbia Broadcasting System and Rutgers University has documented that television's most powerful impact is on children. Youngsters average more than two hours of watching each evening. The most surprising finding was the difference in the hold of television on different social groups: families with little education lose interest in television programs sooner than the better educated."

ENCEPHALITIS-"If our present hypotheses are correct, the encephalitic diseases of man and horses represent possibly the most complex disease cycle so far unraveled. The possible reservoir of the Western equine encephalomyelitis virus is mites, which pass it along to their young and to birds. The principal endemic cycle circulates the virus among birds and Culex mosquitoes. The possible epidemic cycle infects horses and men, who transmit the virus through the Aedes mosquito."

In Focus: The Fallout From Cassini; September 1999; Scientific American Magazine; by Alpert; 2 Page(s)

At 3:28 A.M. Greenwich Mean Time on August 18, the twostory-tall Cassini spacecraft was expected to swoop past Earth, hurtling about 1,170 kilometers (725 miles) over the South Pacific at a blistering speed of 68,000 kilometers per hour (42,000 miles per hour). The flyby maneuver would use Earth's gravity like a slingshot, accelerating the spacecraft to its 2004 rendezvous with Saturn, where it will explore the planet's rings and its 18 known moons.

In the weeks before the flyby, however, critics of the Cassini mission warned of the potential for a nightmarish accident. The spacecraft contains three radioisotope thermoelectric generators (RTGs), which produce electricity from the heat emitted by the radioactive decay of plutonium 238 dioxide. RTGs have provided power for about two dozen spacecraft, including the Voyager and Galileo probes; the devices are particularly useful in the outer reaches of the solar system, where sunlight is too weak to generate much electricity. Critics have focused on Cassini because it holds a record amount of plutonium fuel: about 33 kilograms (72 pounds). More than 1,000 people demonstrated against the mission in Cape Canaveral, Fla., before the spacecraft's successful launch from there in October 1997. In June of this year anti-Cassini groups organized smaller demonstrations against the Earth flyby.

Congo City; September 1999; Scientific American Magazine; by Holloway; 2 Page(s)

It can be so difficult to tell the difference between real and fake at the new Congo Gorilla Forest exhibit at the Bronx Zoo in New York City that even the mandrills get confused. In a recent foray in her new digs, a mandrill mother approached the glass that separates her from zoo-goers. She suddenly assumed a defensive posture and backed off, pulling her baby with her. A lovely bronze sculpture of a rock python-with apparently just the right-looking twist to its neck-on the visitors' side had spooked her. "It was one of the greatest moments that I've had in this exhibit," says project director Lee C. Ehmke. "It is pretty amazing that these zoo-bred mandrills, fourth or fifth generation, are somehow hardwired for snakes."

That kind of realism, and reaction, is exactly what the designers of the justopened $43-million, 6.5-acre exhibit aimed for. And although the monkey's response was unexpected-the bronzes by Priscilla Denaci Deichmann were to be accurate but purely decorative-it illustrates an attention to detail that makes the Congo Gorilla Forest really resemble a mysterious, exhilarating walk through an African rain forest, without the bug bites. To create this exhibit, which is inhabited by 75 different species, the Bronx Zoo team used the techniques of immersion design: the fabrication of naturallooking landscapes and flora and fauna that many zoos started pursuing in the 1980s. But, according to experts in the field, they raised the bar.

Silicone Safe; September 1999; Scientific American Magazine; by Reed; 1 Page(s)

Women who have silicone breast implants are no more likely than the rest of the population to develop cancer, immunological diseases or neurological disorders, a committee of the Institute of Medicine (IOM) reported on June 21. Moreover, mothers with implants may safely breast-feed their infants, as there is no evidence of toxicity in the milk. The IOM committee drew its conclusions after holding public hearings (during which women with implants told of their experiences) and reviewing scientific literature on silicone breast implants (first made in 1962) and silicone.

The analysis-funded by the U.S. Department of Health and Human Services and the National Institute of Arthritis and Musculoskeletal and Skin Diseases-is the latest in a series to have found such results. Similar announcements were made last year by scientists who were appointed by judges overseeing implant liability litigation in the U. S. and by researchers in Britain reviewing implant safety for the British Department of Health.

Calculating Immunity; September 1999; Scientific American Magazine; by Beardsley; 2 Page(s)

The immune system can vanquish bacteria, viruses and cancer cells with an accuracy that puts drugs to shame-if it recognizes them as enemy aliens. But although researchers have learned a good deal about how the body's defensive army is organized, they cannot usually predict exactly how the atomic-level interactions between invaders and defenders will play out and thus which alien proteins will stimulate a response. If the engagement of pathogens' proteins with immune cells could be modeled in detail on computers, laboratory-synthesized molecules could rev up the immune system and induce it to attack recalcitrant tumors and fight incipient infections for which no vaccine now exists.

Today's computers and programs actually have all that it takes to model molecules; the problem is that there are far too many possibilities to sift through them all. The immune system produces thousands of different proteins whose job it is to look out for infiltrators, in any of billions of different combinations. Infiltrators carry a similarly colossal number of molecular identifiers. So the number of ways the two might combine is unimaginably huge. Computers easily get bogged down in problems with vast numbers of possibilities.

In Brief; September 1999; Scientific American Magazine; by Staff Editors; 3 Page(s)

La Nina Continues-The National Oceanic and Atmospheric Administration predicts that the current La Nina will persist into 2000.La Nina is characterized by colder-than-normal areas in the Pacific Ocean,which affect atmospheric flow.For the U.S.,that means a dry winter in the Northeast and the South and a rainy one in the Pacific Northwest.-Philip Yam

But I Own a Porsche...-In what could change the bar scene,investigators say that attraction depends on the menstrual cycle. When conception chances were highest,women seeking a short-term relationship preferred the "masculinized" look of a squarer jaw and wider face,which may indicate good health.During other phases,women favored more feminized faces,attributing to them more positive personality traits. "Selection might have favored human females who pursued a mixed mating strategy" under certain conditions,the authors write in the June 24 Nature.-P.Y.

Strike Zone; September 1999; Scientific American Magazine; by Scott; 1 Page(s)

Airplanes and birds just can't get along. Every year pilots in the U. S. report more than 5,000 bird strikes, which cause at least $400 million in damage to commercial and military aircraft. Although any airborne encounter is going to be harder on the bird (just ask romance-novel cover boy Fabio, who encountered one while riding a roller coaster), the damage the animals can inflict on aircraft control surfaces or engines can lead to disaster. In 1975 a DC-10 taking off from New York City's John F. Kennedy airport ran into a flock of seagulls and lost one of its three engines; the airliner slid off the runway and burned, although everyone on board escaped unharmed. Four years ago the crew of a U.S. Air Force AWACS plane wasn't so lucky. The Boeing 707 lost two of its four engines after striking a flock of geese during takeoff; the crash killed all 24 people on board.

Despite having experimented with everything from electromagnetics to ultrasonic devices to scarecrows, the Federal Aviation Administration (FAA) has yet to endorse one single sensational solution that will keep birds out of the path of an oncoming aircraft. The best bet right now is understanding bird behavior, although an intriguing old pilots' tale-that radar can scatter birds-may carry enough truth to ultimately offer a viable technical solution to a deadly problem.

Anti Gravity: Strife after Death; September 1999; Scientific American Magazine; by Mirsky; 1 Page(s)

Freud said that sometimes a cigar is just a cigar.By the same logic,sometimes a snake is just a snake. Which is good, because I've been thinking a lot about snakes lately. Unprovoked, such contemplation might make me consider analysis of a Freudian nature, but these thoughts have clear inspiration-namely, the New England Journal of Medicine (NEJM) and the U.S. House of Representatives.

NEJM recently carried a letter with the striking title,"Envenomations by Rattlesnakes Thought to Be Dead." The authors, Jeffrey R.Suchard and Frank LoVecchio of the Good Samaritan Regional Medical Center in Phoenix, described five cases of men-only men do dumb stuff like this, apparently-who got the surprise of their life from snakes that had just shuffled off their own mortal coils. Make no mistake,these snakes were as dead as Julius Caesar. "They retain some primitive reflex actions for a short while after being killed," Suchard explains.

Skewing The Cosmic Bell Curve; September 1999; Scientific American Magazine; by Musser; 3 Page(s)

Sometimes it seems that the only thing expanding faster than the universe is cosmologists' bewilderment. Several teams have now reopened what most had thought was a closed case: the random distribution of matter in the nascent universe. Maybe, the researchers say, it is not as random as normally assumed. If confirmed, their findings could rule out inflation, the prevailing model of the early universe-indeed, the only model that has survived decades of winnowing-and set cosmology back 20 years.

Inflation neatly explains the delicate balance of order and randomness in the cosmos: an extra-rapid expansion smoothed out any flagrant unevenness while creating new irregularity, just enough to seed astronomical structures such as galaxy clusters but not so much as to make the cosmos into a bleak web of black holes. The clumping shows up in the snapshot of the infant universe provided by the cosmic microwave background radiation. The radiation has an average temperature of 2.7 kelvins, with deviations of 30 or so microkelvins in different parts of the sky representing slight variations in the density of matter.

By the Numbers: U.S. Immigration; September 1999; Scientific American Magazine; by Doyle; 2 Page(s)

From the founding of the republic to the mid-1920s, U.S.immigration was largely unrestricted,but shortly thereafter Congress passed legislation severely limiting entry from all regions except northwestern Europe. Beginning in 1965 and continuing thereafter, it passed a series of more liberal laws, including the Immigration and Reform Act of 1986,under which 2.7 million illegal aliens, mostly from Mexico,were given legal immigrant status.The new laws not only promoted diversity but also opened the door to the longest and largest wave of immigration ever-27 million since 1965, including illegal entries. Until now, the two largest waves had been from 1899 through 1914, which reached 13.6 million, and from 1880 through 1898, which reached 8.6 million. Not all immigrants stay: in recent years, emigration has been about 220,000 annually.

In 1996, a more or less typical year, there were 916,000 legal immigrants plus an estimated 275,000 who came illegally. Favorite immigrant destinations were California, where one third went, and the New York metropolitan area,which drew about one in six. As a group, immigrants are less skilled and younger than the average American.Of the legal immigrants, 65 percent entered under family reunification programs and 13 percent under employment-based preference programs;14 percent were refugees or asylum seekers. From 1990 through 1998, an average of 460,000 immigrants a year became citizens.

Profile: Defender of the Plant Kingdom; September 1999; Scientific American Magazine; by Beardsley; 2 Page(s)

Peter H. Raven, a man used to looking at the big picture, has a big idea. The 63-year-old scientific diplomat and director of the Missouri Botanical Garden in St. Louis was set in August to call on the world's plant scientists, gathered at an international congress, to save the whole plant kingdom from extinction. Raven, for the past two decades a leading advocate for the preservation of biodiversity, predicts that without drastic action, two thirds of the world's 300,000 plant species will be lost during the next century as their habitats are destroyed. Yet he believes that an international commitment to bring vulnerable species into cultivation in botanical gardens, or into seed banks, could avert the catastrophe. "If you are going to give a single valuable present to the people 100 years from now, then saving all the plants might be a very good way of doing it," he says.

Such a grandiose scheme might sound like an idle fantasy. But Raven is a member of 22 academies of science around the globe and has an impressive history of organizing major projects. (His institution provides the headquarters for a network that is already trying to preserve U. S. plants.) He has just stepped down from a 12-year term as home secretary of the National Academy of Sciences, and he chairs the report review committee of the National Research Council, the operating arm of the academies of science, engineering and medicine. In that role he has overseen formal reviews of some 2,200 studies, many on controversial subjects. Raven is "a very good scientific politician and a good negotiator," says Bruce M. Alberts, president of the science academy.

In Plane Sight; September 1999; Scientific American Magazine; by Dupont; 1 Page(s)

While U.S. and allied fighters and bombers were being hailed for their performance during NATO's Operation Allied Force earlier this year, another, less celebrated type of aircraft was quietly providing a glimpse of the future of warfare. These remote-controlled, pilotless aircraft were used over Kosovo in greater numbers and for more hours than in previous conflicts, and although many were lost, their performance may have solidified their place in the U.S. military arsenal.

As a concept, the use of "unmanned aerial vehicles" for intelligence gathering has made sense for a lot of years and a lot of reasons. UAVs, as the Pentagon calls them, are operated not unlike the hobbyist's remote-controlled airplanes; soldiers on the ground man computer stations with controls that fly the aircraft. Onboard "prying eyes"-cameras, radar, infrared and other sensors-pass intelligence information-target locations, troop movements, battle damage assessments-to the ground station.

Enter Robots, Slowly; September 1999; Scientific American Magazine; by Beardsley; 2 Page(s)

The autonomous robots of science fiction have thus far failed to whir into everyday life: they are too clumsy and expensive for the home, hobbyists aside, and can be tolerated only for the most repetitive tasks in industry. But major development projects are making progress in some of the most difficult areas, thanks to cheaper computing and radio links. "We will begin to see robots more often," says roboticist Takeo Kanade of Carnegie Mellon University.

Although "smart" technology can take numerous forms, almost all mobile robots to date use wheels, a choice that has confined them to a single floor of a building. But Johnson & Johnson, in partnership with inventor Dean Kamen, has recently announced a gyro-balanced wheelchair that can rear up on two wheels, traverse uneven terrain and climb stairs, while keeping its occupant perfectly stable. Kamen says the biggest challenge in the five-year project was ensuring the safety of a user even during a collision or a component failure: the system employs three Pentium-class computers that "vote" on what action to take if an error is detected. The Ibot Transporter is now in clinical trials. Johnson & Johnson is apparently counting on mass manufacturing, because it plans to sell the transporters for as little as $20,000. Advanced battery technology and superefficient motors allow the devices to run for up to a day without needing to be recharged. Kamen is now investigating other possible applications of the stable base.

Not Making Scents; September 1999; Scientific American Magazine; by Nelson; 2 Page(s)

That which we call a rose by any other name would smell as sweet-in Shakespeare's time, that may well have been the case. The rose in its natural state was prized for the fragrant aroma that emanated from its blossoms, but today's modern versions would hardly tickle any Elizabethan's nose. For reasons that are still not clearly understood, floral scent is the number-one casualty of crossbreeding, and many other new varieties of once famously fragrant blossoms have, like the rose, lost their aroma.

Horticulturists introduce about 1,000 new hybrid plants every year, and hybrids now account for about 70 percent of the shrubs currently on the market (and the number is higher for flowers). The goal is to produce flowers with larger and more numerous blossoms, brighter and increased variation of color, resistance to disease, and a long shelf life. Although the loss of floral scent has been recognized for years as a major problem in floriculture, it has been accepted as an inevitable tradeoff for improved market value.

Cyber View; September 1999; Scientific American Magazine; by Grossman; 1 Page(s)

Not many like to think about a chemical disaster like the one in 1984 in Bhopal, India, in which 2,000 people were killed and another 200,000 injured after the accidental leakage of 40 tons of methyl isocyanate from a Union Carbide factory. Even fewer in the U.S. want to think about a similar tragedy happening here. But in 1990 Congress decided the threat was real enough to require an estimated 66,000 industrial sites working with extremely hazardous substances to disclose worst-case accident scenarios. It was all part of risk-management plans that are supposed to cover everything from potential hazards to emergency responses. The intention-reaffirmed as recently as 1997, when the Environmental Protection Agency (EPA) reported similar plans-was to make a searchable database of these risk-management plans available over the Internet.

Some people, however, are concerned that allowing full access to the data to anyone who wanted them, anywhere in the world, might make it easier for would-be terrorists to attack those facilities. Early this year the Center for Democracy and Technology, along with other advocacy groups, raised the alarm after hearing that proposals to limit access to this information were being considered by the House Commerce Committee. In a publicly released letter to the committee's chairman, Representative Thomas J. Bliley of Virginia, the CDT's executive director, Jerry Berman, argued forcefully that the Freedom of Information Act mandates that the information must be supplied in the format requested if it is easily reproducible in that form. Therefore, because the worst-case scenario data will be submitted in electronic form, it must be made available electronically. But on May 13, Bliley introduced House bill HR 1790, the Chemical Safety Information and Site Security Act of 1999. In summary, it says the data would be given mostly on paper to local government officials and to the public under controlled reading conditions, such as in a reference library.

Breathing Life into "Tyrannosaurus rex"; September 1999; Scientific American Magazine; by Erickson; 8 Page(s)

Dinosaurs ceased to walk the earth 65 million years ago, yet they still live among us. Velociraptors star in movies, and Triceratops clutter toddlers' bedrooms. Of these charismatic animals, however, one species has always ruled our fantasies. Children, Steven Spielberg and professional paleontologists agree that the superstar of the dinosaurs was and is Tyrannosaurus rex.

Harvard University paleontologist Stephen Jay Gould has said that every species designation represents a theory about that animal. The very name Tyrannosaurus rex-"tyrant lizard king"-evokes a powerful image of this species. John R. Horner of Montana State University and science writer Don Lessem wrote in their book The Complete T. Rex, "We're lucky to have the opportunity to know T. rex, study it, imagine it, and let it scare us. Most of all, we're lucky T. rex is dead." And paleontologist Robert T. Bakker of the Glenrock Paleontological Museum in Wyoming described T. rex as a "10,000- pound [4,500-kilogram] roadrunner from hell," a tribute to its obvious size and power.

The Teeth of the Tyrannosaurs; September 1999; Scientific American Magazine; by Abler; 2 Page(s)

Understanding the teeth is essential for reconstructing the hunting and feeding habits of the tyrannosaurs. The tyrannosaur tooth is more or less a cone, slightly curved and slightly flattened, so that the cross section is an ellipse. Both the narrow anterior and posterior surfaces bear rows of serrations. Their presence has led many observers to assume that the teeth cut meat the way a serrated steak knife does. My colleagues and I, however, were unable to find any definitive study of the mechanisms by which knives, smooth or serrated, actually cut. Thus, the comparison between tyrannosaur teeth and knives had meaning only as an impetus for research, which I decided to undertake.

Trusting in the logic of evolution, I began with the assumption that tyrannosaur teeth were well adapted for their biological functions. Although investigation of the teeth themselves might appear to be the best way of uncovering their characteristics, such direct study is limited; the teeth cannot really be used for controlled experiments. For example, doubling the height of a fossil tooth's serrations to monitor changes in cutting properties is impossible. So I decided to study steel blades whose serrations or sharpness I could alter and then compare these findings with the cutting action of actual tyrannosaur teeth.

The Dechronization of Sam Magruder; September 1999; Scientific American Magazine; by Simpson; 4 Page(s)

My name is Samuel TM12SC48 Magruder AchA3*. Good old Sam Magruder. Odd that I should want to put down my names and titles first, or to put them down at all. Names are to distinguish us from other men, and I am the only man who exists or ever has existed. Titles are supposedly to label our capacities, really to try to impress our associates. The qualifications of AchA3* have not much bearing on my present life, and my associates here are definitely not impressed. But there it is: I cling to being Sam Magruder. I want to reassure myself that I am I, that this is the same being who is to be born 80 million years from now and registered as Samuel TM12SC48 Magruder. Yet that person does not really exist in any time dimension or universe. He is only going to exist.

I landed up to my waist in mucky water. I was naked as a newborn baby. The timeslip did not work on my clothes or anything around me. It would not have mattered much, anyway, since all I had in my pockets were keys and some money, not exactly useful in the Cretaceous. The clothes themselves would have been useful at first, but would not have lasted long.

Migrating Planets; September 1999; Scientific American Magazine; by Malhotra; 8 Page(s)

In the familiar visual renditions of the solar system, each planet moves around the sun in its own well-defined orbit, maintaining a respectful distance from its neighbors. The planets have maintained this celestial merry-goround since astronomers began recording their motions, and mathematical models show that this very stable orbital configuration has existed for almost the entire 4.5-billion-year history of the solar system. It is tempting, then, to assume that the planets were "born" in the orbits that we now observe.

Certainly it is the simplest hypothesis. Modern-day astronomers have generally presumed that the observed distances of the planets from the sun indicate their birthplaces in the solar nebula, the primordial disk of dust and gas that gave rise to the solar system. The orbital radii of the planets have been used to infer the mass distribution within the solar nebula. With this basic information, theorists have derived constraints on the nature and timescales of planetary formation. Consequently, much of our understanding of the early history of the solar system is based on the assumption that the planets formed in their current orbits.

Repairing the Damaged Spinal Cord; September 1999; Scientific American Magazine; by McDonald; 10 Page(s)

For Chinese gymnast Sang Lan, the cause was a highly publicized headfirst fall during warm-ups for the 1998 Goodwill Games. For Richard Castaldo of Littleton, Colo., it was bullets; for onetime football player Dennis Byrd, a 1992 collision on the field; and for a child named Samantha Jennifer Reed, a fall during infancy. Whatever the cause, the outcome of severe damage to the spinal cord is too often the same: full or partial paralysis and loss of sensation below the level of the injury.

Ten years ago doctors had no way of limiting such disability, aside from stabilizing the cord to prevent added destruction, treating infections and prescribing rehabilitative therapy to maximize any remaining capabilities. Nor could they rely on the cord to heal itself. Unlike tissue in the peripheral nervous system, that in the central nervous system (the spinal cord and brain) does not repair itself effectively. Few scientists held out hope that the situation would ever change.

A Case against Virtual Nuclear Testing; September 1999; Scientific American Magazine; by Paine; 6 Page(s)

In August 1945 the world's first military use of atomic bombs swiftly killed 210,000 people in the Japanese cities of Hiroshima and Nagasaki. In the ensuing decades, humanity's concentration into megacities and the vastly increased power of thermonuclear weapons have elevated the lethality of a single act of atomic violence by roughly two orders of magnitude. Today one or two nuclear weapons detonated over Bombay or Tokyo could instantly annihilate some 15 million people.

With the end of the cold war, many nations came together to negotiate a treaty permanently banning nuclear explosions worldwide. By barring explosive tests, the Comprehensive Test Ban Treaty severely constrains the way nations have traditionally evaluated changes in bomb designs and confirmed the performance of weapons to be stockpiled for military use. A ban on test explosions cannot alone prevent the spread of nuclear weapons, but it does pose a significant barrier to the development of weapons that rely on fusion reactions, including lighter, more compact and more powerful missile-borne nuclear warhead designs, such as those China has allegedly acquired from the U.S. through espionage and intelligence-gathering.

The Throat Singers of Tuva; September 1999; Scientific American Magazine; by Levin, Edgerton; 8 Page(s)

From atop one of the rocky escarpments that crisscross the south Siberian grasslands and taiga forests of Tuva, one's first impression is of an unalloyed silence as vast as the land itself. Gradually the ear habituates to the absence of human activity. Silence dissolves into a subtle symphony of buzzing, bleating, burbling, cheeping, whistling-our onomatopoeic shorthand for the sounds of insects, beasts, water, birds, wind. The polyphony unfolds slowly, its colors and rhythms by turns damped and reverberant as they wash over the land's shifting contours.

For the seminomadic herders who call Tuva home, the soundscape inspires a form of music that mingles with these ambient murmurings. Ringed by mountains, far from major trade routes and overwhelmingly rural, Tuva is like a musical Olduvai Gorge-a living record of a protomusical world, where natural and human-made sounds blend.

Scientists and Religion in America; September 1999; Scientific American Magazine; by Larson, Witham; 6 Page(s)

A stone's throw from the Potomac River in Washington, D. C., a bronze statue of Albert Einstein reposes in a garden beside the National Academy of Sciences. Could there be a more fitting individual than this mythic figure to symbolize the highest echelon of scientists in America?

Having fled to the U.S. from the secular horrors of Nazi Germany because of his religious heritage, Einstein never ceased musing about religion and once challenged quantum uncertainty by famously denying that God plays dice with the universe. Late in life, however, he concluded, "In their struggle for the ethical good, teachers of religion must have the stature to give up the doctrine of a personal God."

The Amateur Scientist; September 1999; Scientific American Magazine; by Carlson; 2 Page(s)

Replenished by the thousands of thunderstorms that constantly pummel our planet, the earth's electric charge produces an electric field that is typically around 100 volts per meter of elevation and that can surge to thousands of volts per meter when a thundercloud rolls overhead. In my July column I explained how to measure these fields with a delightful instrument called a field mill. I also mentioned that we would all be electrocuted instantly were it not for the fact that the atmosphere contains very little free charge (ions and unattached electrons), and so these large fields simply cannot generate dangerous currents. In this issue I thought I would show you how to measure the density of these charges.

Every fraction of a second, cosmic rays strip electrons from some of the normally neutral molecules in our atmosphere. Ionization is also triggered by ultraviolet light, fires and the radioactive decay of certain elements. These processes leave some air molecules positively charged while simultaneously creating a diffuse mist of electrons, some of which are picked up by other atoms. The atmosphere thus contains both positively and negatively charged ions.

Mathematical Recreations; September 1999; Scientific American Magazine; by Stewart; 3 Page(s)

The ancient art of string figures appeals to many recreational mathematicians, even though it isn't overtly mathematical. I chose the title "Cat's Cradle Calculus Challenge" [December 1997] for my last column on string figures to raise the possibility of developing a system to describe their intricate geometry. My confidence that the subject really was mathematical was rapidly justified by a series of communications from readers, including members of the International String Figure Association. Some of these letters explained various systems of mathematical notation for string figures. One letter, however, raised an unanticipated topic: the connections between string figures, mathematics and dance.

There are plenty of links between mathematics and the arts: the use of perspective in painting, for example, or the ratios that occur in musical scales. But the only connection between mathematics and dance that I had previously seen was an analysis of the symmetries of English country dancing carried out some years ago by my colleague Chris J. Budd, a mathematician at the University of Bath. The letter-from Karl Schaffer, co-founder of the Dr. Schaffer and Mr. Stern Dance Ensemble in Santa Cruz, Calif.-told me about something very different: the conscious use of mathematics to create dances. Schaffer detailed several dances based on the use of loops of string to construct regular polyhedra and other mathematical figures.

Reviews; September 1999; Scientific American Magazine; by Morrison, Staff Editors; 3 Page(s)

Space probe Voyager I launched in 1977, its appointed scans completed, drifted for a dozen years out past Neptune. In 1990 NASA unexpectedly radioed, "Look back, Voyager." Six light-hours out from the sun, snap those planets now in view. From there Earth is seen as a featureless bluish dot, like what the unaided eye has always made of the other planets. In Carl Sagan's visionary 1994 book entitled Pale Blue Dot, you can see for yourself that unifying view of Earth among its sibs.

His text accompanying the photograph runs: "On it everyone you love...every human being who ever was, lived out their lives...every hunter and forager, every hero and coward, every creator and destroyer of civilization, every king and peasant...every 'supreme leader,' every saint and sinner in the history of our species lived there-on a mote of dust." Carl was not only its eloquent assayer but a major proponent of the belated effort that finally brought Earth to pose among the other planets. He was directly engaged in the task Pale Blue Dot celebrates. Personal persuasion allowed his originality to act in institutions as complex as NASA. His presence would rise to high celebrity, reaching even the comic strips, and glow on video screens the world around-though not yet 10 parsecs out.

Connections: Or Maybe Not; September 1999; Scientific American Magazine; by James Burke; 2 Page(s)

With all the academic research available these days about what it was really like back in the Dark Ages when the European cultural lights went out (or maybe not), it's a pity Hollywood continues to churn out all that anachronistic garbage about King Arthur. You know-people using terminology from 900 years later, knights in fancy armor (from 700 years later), coats of arms and chivalry (600 years later), turreted castles with drawbridges (600 years later), riders using stirrups (500 years later) and so on.

Mind you, clearing up these anachronisms would probably go over like a lead balloon at the box office. Which is how it went with one of history's greatest exposes of a similar nature. The box office in question was that of the Catholic Church, whose 15th-century boss was a pope with as much political clout as spiritual. Or so he thought. Till in 1440 a philological scribbler (a.k.a. humanist scholar) named Lorenzo Valla went looking for a bit of dirt on the papacy (his boss, the king of Naples, was having a row with the Vatican about who ruled what). Valla used his Latin smarts to point out that the language and terminology used in the hitherto unquestioned document of the Donation of (Byzantine emperor) Constantine-which had given the Roman pope secular authority over Europe-were (like the language and terminology of Hollywood King Arthur screenplays) bogus and that the donation was a fake, written 400 years after the supposed event. Which of course blew away the pope's claim to temporal power. Everything Curial hit the fan.

Working Knowledge; September 1999; Scientific American Magazine; by Silberman; 1 Page(s)

Architects design stadium roofs that open and close so that playing fields can be planted with natural grass instead of hard Astroturf. Protecting fans and players from the elements remains a secondary consideration. Since building the first one-the Toronto Skydome in 1989-designers have crafted many types of retractable roofs. Some roofs, for instance, open over only a small central section. The multipaneled movable roof of Enron Field (shown below), where the Houston Astros are scheduled to play ball next year, will expose more sky than any other stadium does. The roof will retract completely off the ballpark, uncovering even a glass-walled section of the outfield so that Mark McGwire or another slugger can hit one out of the ballpark.