Ken Alder: The Measure of All Things

By PAT BASKETT

How long is a metre? That's not a silly question. The answer: one ten-millionth of the distance from one pole or the other to the Equator. Two Frenchmen devoted seven years to ascertaining that exact measurement, from 1792 to 1799.

Jean-Baptiste-Joseph Delambre and Pierre-Francois-Andre Mechain didn't travel from the North Pole to the Equator. They measured a section of the meridian arc that runs from Dunkerque through Paris to Barcelona, and computed the distance from their calculations. Delambre started from Dunkerque, Mechain set out from Barcelona.

These were years of extreme political uncertainty following the French Revolution of 1789, and France was at war with Spain, England and Prussia.

The two men with their geodesic equipment and their assistants were each taken for spies. Mechain was detained in Spain. But their devotion to the task of measuring the Earth, as they called it, was absolute and this, in a sense, is what the book is about: the pursuit of truth or, at least, of knowledge.

It caused Mechain's death in a malaria-infested part of Spain. He was agonising over an error in his calculations which he had been at pains to conceal, not through lack of scruple but because he needed to understand its cause. He had left his family in Paris, his wife carrying out his duties as an astronomer.

Delambre was a single-minded bachelor. Both were men of modest origins and high intelligence.

As well as giving us the history of the metric system, this book is about the intellectual environment at the end of the Age of Enlightenment and the extraordinary minds of those who saw science as ushering in a new era. (One of the most famous astronomers was an atheist who ate spiders.) Alder persists in referring to them by the French term "savant" which sits uneasily, to my mind, in his otherwise smooth-flowing prose.

They made grand claims for the benefits to humanity of a metric system of measurement derived from nature, rather than the inconsistent one deriving from the vicissitudes of social and commercial intercourse.

Ironically, these claims failed to convince their compatriots and Napoleon refused to learn it. The metric system was not adopted in France until 1840.

The United States is almost the only country in the modern world that has still not seen its advantages - to its cost. The Mars Climate Orbiter was lost in 1999 because a Nasa investigation revealed that one team of engineers had used traditional American units while another had used metric units, causing a trajectory error of 60 miles.

Alder extracts every possibility from this fascinating story (and includes every possible footnote) and the result is a gold mine for those interested in the history of science. The less scientifically literate, however, may feel a little overwhelmed at times.

Little, Brown

$39.95

* Pat Baskett is an Auckland journalist.