Plus or Minus One Ear
- World in the Balance: The Historic Quest for an Absolute System of Measurement by Robert Crease
Norton, 317 pp, £18.99, October 2011, ISBN 978 0 393 07298 3
The geeks at the Massachusetts Institute of Technology are fond of merry japes, locally known as ‘hacks’. One of the more memorable happened one night in October 1958 when an MIT fraternity had the idea of initiating new members by making them measure a bridge over the Charles River connecting the Cambridge campus with Boston. Crossing the bridge was often a wet, windy and unpleasant business and it was thought that students returning at night from downtown would like to know, by visible marks and with some precision, how far they still had to go. The older fraternity brothers decided to use one of the new pledges as a rule, and selected Oliver R. Smoot, the shortest of the lot at 5ft 7in. The other pledges laid Smoot out at one end of the bridge, marked his extent with chalk and paint, then picked him up and laid him down again, spelling out the full measurement every ten lengths, and inscribing the mid-point of the bridge with the words ‘halfway to Hell’. In this way, it was determined that the span was 364.4 smoots long, ‘plus or minus one ear’ (to indicate measurement uncertainty).
Vol. 34 No. 18 · 27 September 2012
From Emma Tristram
In his list of not-yet-standardised measuring systems, Steven Shapin could have added the phenomenon of ‘vanity sizing’, whereby the actual sizes of garments have increased over time relative to their nominal size (LRB, 30 August). This practice entails lying about the measurements used, in order (presumably) to sell more clothes to people who want to imagine themselves thinner than they might be. It’s very annoying.
Arundel, West Sussex
Vol. 34 No. 20 · 25 October 2012
From Ollie Brock
Steven Shapin skips quickly past what ought to be a cornerstone of his subject, the international prototype for the kilogramme (LRB, 30 August). It is a relic of a previous metrological era, being the sole surviving measurement derived from a manmade object. Seated in a laboratory just outside Paris and known to its carers as ‘le Grand K’, it was described by Mary Bowers in India’s Caravan magazine as being ‘hardly bigger than an apricot’.
Most of the experts Bowers consulted were optimistic at the time that the quadrennial conference of the Bureau International des Poids et Mesures (BIPM), held in 2011, would adopt a physical constant to replace the ageing prototype. In the end, the conference postponed the decision to its next meeting. Robert Crease, whose book Shapin is reviewing, says that the problem is weight loss ‘due to the escape of bubbles’ trapped in the metal. But Bowers quotes Richard Davis, the physicist in charge of the model, saying that the sister prototypes against which ‘le Grand K’ is measured could instead be getting heavier. Even if the kilogramme is losing mass, he told her, ‘there aren’t any serious theories’ as to the reason, only ‘possibilities’ – the evolving-out of hydrogen bubbles being one of them. ‘Others blame the cleaning process,’ Bowers wrote, ‘which has not been changed in over a century and still involves wiping the object manually with alcohol and a soft cloth.’