We look ahead to the 400th anniversary of an innovation that simplified the measurement of land area, initially in England and later in the UK, by introducing decimals.
Today when we measure land area the calculation is straightforward. Consider a minimum sized football pitch, defined as 90 x 45 metres or 100 x 50 yards.
In metric, area = 90 x 45 = 4050 sq m = 0.405 hectare.
In Imperial, area = 100 x 50 = 5000 sq yards = 5000/4840 acre.
Dividing by 4840 is simple, so long as you have a calculator or smart phone to hand. It was less so four centuries ago, before the arrival of electronic and mechanical calculators, the slide rule and logarithms.
Step forward English clergyman and mathematician Edmund Gunter, 1581–1626, who developed a chain, 22 yards long with 100 links. Ten of his chains made a furlong, which, like the rod and the acre, had enjoyed legal recognition since the late thirteenth century. A furlong was 40 rods, and one acre was equal to 160 square rods, or using Gunter’s system ten square chains, hence 100 000 square links.
Back to our modern football pitch. Using Gunter’s chain, the pitch would measure about 4 chains 54 links (4.54 chains or 454 links) by 2 chains 27 links (2.27 chains or 227 links).
Area = 454 x 227 = 103 058 sq links = 1.03 acres.
Gunter’s chain, which he introduced in 1620, became extremely popular. Railway surveyors and engineers in the 19th century used Gunter’s chain for setting out – much of the line from London to Reading, constructed in the 1830s, is at a gradient of 1/1320 or 1 foot in 20 chains. Readers who use British railways may also have noticed markers on bridges and other structures, for example “91 m 56 ch”. And the length of a cricket pitch is, of course, one chain.
When sorting through my dad’s tool box a few years ago, I came across a “modern” equivalent of Gunter’s chain – a linen tape. A link is 7.92 inches, as this photo illusrates.
When we think of pioneers in the simplification of England’s arcane measures, a name that comes to mind is John Wilkins, 1614-1672, first Secretary of the Royal Society, who proposed a decimal system. But his proposal was never followed up in England whereas Gunter’s innovation was quickly adopted. It dramatically simplified the calculation of land area, and survived well into the twentieth century until overtaken by technological developments and the UK’s metric changeover.