Numbers

PITY the poor kilogram. At the International Bureau of Weights and Measures at Sevres in France, there is a platinum-iridium cylinder that weighs exactly one kilogram. That is how the kilogram is defined. Once it had the company of the standard metre, which, until 1960, was the length of a metal bar in Sevres, but now the kilogram is all alone, the last scientific unit to correspond to a tangible object.

The metre, originally 1/10,000,000th of the distance from the North Pole to the Equator, is now the distance light travels in a vacuum in 1/299,792,459th of a second. And a second, which we all thought was a 60th of a minute, which was a 60th of an hour, which was a 24th of a day, which was the time it took the earth to spin once on its axis, is now defined as the time it takes for 9,192,631,770 cycles of resonance vibration of the caesium-133 atom.

You knew where you were with the old units. A fathom was the distance between the middle fingers with both arms stretched (from the Old English verb faethmian, to hold with both arms); an acre was the area of land that one yoke of oxen could plough in a day; a mile was the Roman mille passus, a thousand double- paces; and a foot, even if it had to be almost a size 14 to fit, was very vaguely the length of a foot.

Science, in its search for ever- increasing accuracy and truth, has taken all everyday relevance from our units of measurement. Let us hold high the last remaining kilogram and preserve it from redefinition in terms of electromagnetic cycles of thingummybob.