Dr. Fred Bortz

THE SCIENCE SHELF

A TALE OF TWO PLANETS
by Fred Bortz

(September-October, 2002)


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Also recommended on The Science Shelf: coverThe World of Gerard Mercator: The Mapmaker Who Revolutionized Geography by Andrew Taylor


It was the best of times; it was the worst of times. It was a time of revolution; it was a time for resolution. It was a time for precision; it was a time for speculation. It was a time for caution; it was a time for risks.

It was a time for map-makers.

Those themes, played out by real characters worthy of a Dickens novel, pervade two new books about the surveying of two planets: Earth at the end of the eighteenth century and Mars at the beginning of the twenty-first.

THE MEASURE OF ALL THINGS

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In 1792, as revolutionary fervor spread throughout France, two geodesers, experts in the measurement of the Earth, set out from Paris in opposite directions to measure the polar circumference of the planet with a precision never before achieved. As Ken Alder describes in The Measure of All Things: The Seven-Year Odyssey and Hidden Error That Changed the World (Free Press, $27.00, 416 pages, 2002) , their motivations were scientific but their task was political.

The circumference thus determined would become the basis of a world-wide standard of measurement in the new, rational, democratic order, the metric system. The standard of length would no longer be based on local custom or one royal's body part. It was to be exactly one ten-millionth of the distance along a meridian from the North Pole to the Equator of everyone's Earth.

So Jean-Baptiste-Joseph Delambre headed north toward Dunkirk, while his south-going partner, Pierre-Francois-Andre Mechain, set off for Barcelona. The task, though demanding, should have been completed in months, but it took seven years.

The setbacks were sometimes due to political turmoil, geography, or weather. More often, Mechain's melancholy and his perfectionist streak caused complications. So did some locals who impeded the work because standards of measure would lead to both taxation and loss of control over the local economy.

The heart of this story lies in discoveries from Mr. Alder's research, done largely by bicycling the route of the two geodesers. He found a cache of their private letters, still under the seal that Delambre had affixed not long before his death -- secrets he deemed best left for posterity.

Mechain, it turns out, believed he had made a critical error while determining the latitude of the southern endpoint. He covered it up, hoping to be able to repeat the measurement. In his three-volume account of the mission, Delambre chose not to reveal Mechain's deception. A universally accepted standard meter and Mechain's reputation were more important than whether the polar quarter-circumference was exactly ten million meters.

By modern measurements, that arc is 10,002,290 meters long, but the difference has more to do with Earth itself than with error -- hidden or otherwise -- in the geodesers' logs. And as for the discrepancy that so haunted Mechain, there's an irony that is too delicious for a reviewer to reveal.

MAPPING MARS

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Maps are more than diagrams on paper. They convey a sense of time, place, and movement. People look at maps and see stories.

So it has been with Mars from the time astronomers began gazing at it through telescopes and observing its changing features. In Mapping Mars: Science, Imagination, and the Birth of a World (Picador, $30, 368 pages, 2002) , Oliver Morton captures the revolutions in thought that come from envisioning another world and comparing it to our own.

Before telescopic photography, astronomers viewing Mars would sketch what they saw, trying to be faithful yet burdened with the human gift of interpretation. In 1877, Giovanni Schiaparelli saw and drew many actual geographical features; but some, particularly the canali (channels), were artifacts of his perceptual system.

It was natural for his brain to connect the dots. It was equally natural to imagine that the channels carried water, especially since the planet's seasonal color changes suggested that it supported vegetation.

Twenty years later, Percival Lowell drew his own maps and his own conclusions. In his mind, channels became canals, engineered by a civilization desperate to sustain itself on a dying world. His vivid descriptions captivated average citizens, angered skeptical scientists, and inspired science fiction writers.

Spacecraft of the 1960s and 1970s produced images with greatly improved resolution, sniffed the planet's atmosphere, analyzed its soil, and changed both maps and stories. Mars became a geologically inactive, cratered desert, lifeless now and always.

At century's end, planetary news included tantalizing yet disputable evidence of fossils in a meteorite from Mars. Pathfinder and its rover, Sojourner Truth, explored the likely site of an ancient Martian flood, and new orbiters produced detailed relief maps that suggested both a water cycle and vulcanism. (See the review of Managing Martians by Donna Shirley, also on this site.)

New stories arose with new champions, proposing affordable technologies that will enable people to establish Mars bases, then colonies, then a planet engineered to sustain an Earth-like ecosystem. Imagine the maps those pioneers will draw, Mr. Morton says, and imagine the stories those maps will tell.

ABOUT THE COLUMNIST

Dr. Fred Bortz's book Techno-Matter: The Materials Behind the Marvels recently won the 2002 American Institute of Physics Science Writing Award for works intended for children.