Earth and Space

The Great British Mass Standard

Stories from Physics for 11-14 14-16 IOP RESOURCES

Historical accounts report that a mass standard pre-dated the Norman Conquest and was referred to as the pound of the Tower of London. No physical examples of the Tower pound survive, though a bell-shaped brass weight matching the mass of the pound was found in Westminster Abbey in 1842 but has since been lost.

Whilst the Magna Carta called for further harmonisation – ‘There shall be standard measures of wine, ale, and corn (the London quarter), throughout the kingdom’ – standardisation came slowly. James Watt complained of the problem when communicating with scientists in Europe: ‘I had a great deal of trouble in reducing the weights and measures to speak the same language; and many of the German experiments become still more difficult from their using different weights and different divisions of them in different parts of that empire’.

Watt’s imperialist solution to the issue was for all nations to adopt the pound as a unit of measurement arguing: ‘for the utility is so evident, that every thinking person must immediately be convinced of it’. However, he was not entirely satisfied with the existing system and proposed redefining the pound so it consisted of 10 ounces or 10,000 grains.

In 1834, the Imperial prototype masses were destroyed in a fire at the Houses of Parliament and in 1844 a new platinum prototype was produced. The British pound prototype was kept in a temperature controlled vault and lifted using an ivory fork.


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