Who Decided How Long a Metre Is? AfterMaths Summer Special 3

Who decided how long a metre should be? Why is a mile 1,760 yards? And what connects the French Revolution, an expedition from Dunkirk to Barcelona and the speed of light?

In this AfterMaths Summer Special, Jon and Becky explore the messy, surprising and occasionally bewildering history of measurement.

They begin in a world before standard units, when lengths were measured using hands, feet, cubits, spans and paces. These methods were convenient and widely understood, but rather less useful when accuracy mattered and everybody’s body produced a different answer.

From there, they investigate the historical accumulation that gave us imperial units, including the supposed connections between inches and barleycorns, feet and actual human feet, and miles and Roman paces.

The story then moves to revolutionary France, where mathematicians and astronomers attempted to create a universal decimal system based on the dimensions of the Earth. Their effort to establish the metre involved years of surveying, triangulation, political upheaval, arrests and the inconvenient discovery that neither the Earth nor their measurements were quite as perfect as hoped.

The metre was later represented by a platinum-iridium bar, then by a wavelength of light and, finally, by the distance light travels through a vacuum in a precisely defined fraction of a second.

It is a journey from body parts to universal constants, with plenty of mathematical history, questionable conversions and the inevitable disagreement about whether a pace and a “dolly step” are the same thing.

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Thanks for listening, and as ever, keep doing the maths.