The lengths some will go to...

In its attempt to do away with irrationality, the French revolution targeted the morass of units of measurement that complicated French life.

They were unpopular, an invitation to fraudulent tradesmen and, worst of all, illogical.

The metric system that replaced them is the best remembered of the revolution's reforms. The calendar was restructured into 30-day months containing three ten-day "weeks", the day was allotted ten 100-minute hours, and the right angle was chopped into 100 degrees instead of 90.

Ken Alder's story of this is built around the epic tale of Jean-Baptiste-Joseph Delambre and Pierre-François-André Méchain, the two astronomers entrusted with what their sponsors described as the most important mission in the history of science. Although their task began under the monarchy, its real importance came from the revolutionaries'

insistence on relating metric units to the size of the earth itself. The length of arc from pole to equator would be defined as 10 million metres and, since a cubic metre of water would by definition weigh a tonne, length would define mass.

Delambre and Méchain were told to measure the earth's circumference. The method was to determine the length of France from sea to sea, north to south, find the latitude at each end, and multiply up to get the answer.

New technology was available to make the process more accurate than in the previous attempt several decades earlier.

The book conveys the chaos of revolutionary France to perfection. Both men risked death from locals who assumed they were spies, royalists or other forms of traitor. Hyperinflation destroyed their money, and the wars of revolutionary Europe came close to undoing their work. A north-south line through France from Dunkirk reaches the sea, then as now, at Barcelona, in Spain rather than France. As the two countries were at war, this made surveying the front line tricky, especially as there were army officers in the French party. Signal fires for night work were particularly likely to be misunderstood. War trapped Mechain in Spain for years, and he eventually got home via Italy.

In fact, Barcelona is where his project came unstuck. He made an error, which means that the metre was wrong by about the thickness of a sheet of paper. This drove him to deep despair, and he eventually died of malaria while extending the survey line from the mainland to the Balearic Islands.

But even with perfect political conditions, the survey would have been ambitious. It demanded feats of organisation to get massive equipment to mountain tops, brilliant experimental skill and the patience to wait for clear weather. Despite these barriers, the distance was measured to within a few feet.

The politicians behind Delambre and Mechain had ambitions beyond the borders of France. They launched the metric system - today called the Système Internationale (SI) - at the world's first international scientific congress in 1799.

In 1863, the House of Commons voted to make metric units standard throughout the British empire, although the parliamentary session ended before the bill could get through the House of Lords. In the US, the units are widely hated but are making stealthy progress. In science and technology they have long since defeated their rivals.

Alder's research is formidable and he writes stylishly on a complex topic.

As he sees it, the founders of the metric system were in some ways the forerunners of today's enthusiasts for globalisation. In exile in St Helena, Napoleon himself rubbished the system, saying that its founders were "trying to sign up the whole universe" to their project. They would probably have regarded this as a compliment.

Martin Ince is contributing editor, The Times Higher .