This 16th-century woodcut shows how weighing with a steelyard can be mathematically analysed

Metrication: a matter of national identity

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With the UK government consulting on the partial restoration of imperial units, it is worth reflecting on the country’s fraught relationship with metrication – and the engineers who were almost always a step ahead.

It was not all that long ago that a unit of grain could differ almost from one village to the next. This worked in a smaller, pre-industrial world, or at least it worked well enough. In a world of cross-border trade and empirical scientific practice, it was no longer tenable.

The Scientific Revolution brought about a new approach to science based on increasingly quantitative observations. An epistemological debate emerged about how we could measure nature, and hence comprehend it. There were many questions that needed answering – such as how to measure previously unmeasured quantities like heat – but perhaps the most important was the question of standardisation. The Scottish engineer James Watt proposed a standard decimal measurement system in 1783 in the hope of removing barriers to collaboration with European scientists.

“The science practitioners, especially in chemistry, were turning towards more quantifiable measures and methods,” says Emma Prevignano, a PhD candidate at the University of Cambridge specialising in the unification of weights and measures in 18th-century France. “They were communicating data with colleagues abroad and would have liked to speak the same language, in a way.”

James Watt

Scottish inventor James Watt

Image credit: Gettyimages

In 1790, the French National Assembly put out an invitation to join its efforts to establish a standard decimal measurement system based on the seconds pendulum. This was warmly received in Britain, where the idea of a pendulum-based measurement system had been proposed more than a century before. At this time, the main impetus for the standard measurement system was pursuit of a “friendly project” with Britain with ease of scientific collaboration at its heart, Prevignano explains.

The timing of the project, however, could not have been less auspicious, and the overthrow of the French monarchy soon scuppered all chance of collaboration with Britain.

The metric system – based on painstaking measurements by the Académie des Sciences of the Earth’s meridian, passing near Paris – was adopted in France in 1793. This decision is best understood in the context of the Revolution. Prevignano explains that the system “spoke quite well to the revolutionary spirit” in its rejection of a feudal system of local units controlled by lords. It was intended to give ordinary people agency by making them “self-sufficient in calculations related to their interests [...] without which they cannot be really equal in rights”. Though universal, the system is still considered French.

“The metric system is associated with the excesses of the Revolution, particularly with the idea of an overthrow of the natural order, extending to divine right of kings, and units that have grown out of hundreds of years of use,” says James Vincent, author of ‘Beyond Measure: The Hidden History of Measurement’.

Napoleon’s downfall marked a turning point in Anglo-French relations. The adoption of the metric system was discussed in the UK Parliament in 1818, though many generations would pass before it could bring itself to so much as acknowledge the system.

Indeed, policymakers took a passive role throughout the Industrial Revolution while scientists and engineers moved ahead with drafting and recognising the measurement standards required to do their jobs in an increasingly globalised world. British scientists and engineers were among the strongest proponents of standardisation and decimalisation, and thus of the metric system (although some entertained the prospect of decimalised imperial units). Mechanical engineer Joseph Whitworth, for example, advocated standardisation and decimalisation and showed off his precision measuring machine, which could measure to within one-millionth of an inch, at the Great Exhibition of 1851. In 1861, a committee of the British Association for the Advancement of Science – its members including Maxwell, Kelvin and Joule – were assigned the task of investigating ‘Standards of Electrical Resistance’. Its first report proposed new units of electromagnetism and adoption of the metric system.

“There are these debates within the sciences,” says Dr Aashish Velkar, an economic historian at the University of Manchester who has investigated the historical processes through which measurement standards are developed. “They realise that length, weight and volume are not going to be sufficient; they need to add all these other fundamental units as well, like electrical resistance.”

It is unsurprising that it was among these communities that there was most interest in measurement reform. Scientific discovery has always been bounded by instrumentation: from the telescopes through which distant planets were first observed to the hyper-precise Laser Interferometer Gravitational Wave Observatory which captured the faint echoes in spacetime caused by the collision of black holes billions of light-years away. The desire to improve the practice of measurement was strongest for emerging fields like electrical engineering, in which the need for precision and consistency – as well as for entirely new units of measurement – was most palpable.

Velkar acknowledges a division in attitudes between the engineers working in older and younger fields: “Civil engineers liked the imperial system, whereas electrical engineers were thinking about the metric system because they want their measurements to be a lot more precise,” he says. In a similar vein, older industries such as textiles tended to be more cautious about the metric system while those based on newer technologies (e.g. chemicals) had fewer qualms.

The UK Parliament conceded to legalise metric units in the Weights and Measures Act 1897. By the mid-20th century, the political debate had barely shifted, and imperial units remained the default for everyday transactions – although scientific and (most) engineering communities had long since adopted the metric system.

The political will to metricate only came when it could no longer be denied that the British Empire was in terminal decline. “From a political perspective, it’s once Britain realises that its economic future is dependent on closer ties with Europe – not just with America or the Commonwealth – that there are serious studies being done within the government to see how feasible it is to move towards the metric system,” says Velkar. The UK’s gradual transition began in 1973 when it joined the European Economic Community and consented to align with its neighbours.

In certain ways, the UK was dragged kicking and screaming towards metrication; the use of ‘supplementary indications’ (use of equivalent imperial units) continued far longer than intended due to public resistance to their removal. Logical arguments for metrication can fall flat in the face of a nationwide emotional attachment to imperial units, which seem to evoke an inexplicable sense of organicity and a more explicable sense of Britishness (especially when compared with the seemingly technocratic and French metric units). Imperial units are more than a nostalgic element of national identity. They are associated with a time when the British Empire quite literally ‘ruled’ its colonies in imperial units: an age that a vocal part of the population looks back on fondly.

Such is this strength of feeling that the UK’s metrication story, centuries later, is still not concluded. In June, the UK government announced a consultation into the partial restoration of imperial units (permitting them to be shown with greater prominence in consumer goods labelling). Though hardly a full-throttle return to imperial units, it has been derided as a distraction by industry groups. Vincent considers the consultation, “part of the Conservative Party’s nostalgia project”, much like navy-blue passports. “The reason this was suggested is because of the deep cultural history associated with measurement,” he emphasises.

 Mars Climate Orbiter Mission

Mars climate orbiter

Image credit: Gettyimages

As for scientists and engineers, the consultation has little relevance; these communities are largely self-regulated with regards to measurement units. However, engineers have cautioned against any backsliding towards imperial units for similar reasons as in centuries past – it complicates collaboration, now with potentially disastrous consequences. For instance, in 1999, Nasa’s $125m Mars Climate Orbiter was destroyed as a result of engineers not converting between imperial and metric units in navigation commands sent from Earth, causing the spacecraft to fall into the Martian atmosphere and disintegrate.

A blog post by the Institution of Civil Engineers calls for a full review of safety implications before imperial units could be so much as countenanced in engineering: “Modern engineering systems are highly complex and difficult to integrate, with too many opportunities for misunderstanding and miscommunication,” it says. “This can lead to errors, potentially leading to difficult rework, additional expenses and/or delays. In particular situations, it can lead to public safety issues caused by confusion. Making this situation worse by the introduction of a parallel system of units will lead to more project delays and cost overruns. Potentially, in some situations, it could also compromise safety – possibly in quite serious ways.”

It would be naive to conceive of this story as a battle of logical scientists and engineers arguing for metrication, and emotional nationalists pushing back against it – after all, scientists and engineers can be as given to nationalism as the rest of us. However, the needs of technical fields have meant that scientists and engineers have tended to charge ahead while political debate on legal metrology follows behind. Now, it may be fair to say that the political debate is not so much following behind as turning back to look wistfully to the past. 

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