Editorial Feature

The Measure of All Things: A Brief History of Metrology

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Metrology is defined as the science of measurement. Metrology dates back to the ancient world, but modern metrology is derived from the politics French revolution, where the standardisation of units was introduced.

Metrology can be split into different activities. The first activity defines the units of measurement, the second puts the units of measurement in practice, and the last applies them to traceability. Metrology can also be divided into further sub-fields of scientific, applied, industrial, technical and Legal metrology.

Metric Systems of the Ancient World

The system of measures, which is at the basis of all metric systems of the ancient world and China, was conceived prior to the appearance of cuneiform writing in Mesopotamia in approximately 2,900 B.C.

The system of measures dates as far back as 6,000 B.C., when it became necessary due to agricultural development needing to calculate the distribution of crops and the volume of food consumed by families. With the transition of humankind from nomadic groupings to established agricultural settlements, metrology was imperative in managing population growth and confronting famine.

It was not until 1875 at the Metre Convention  that scientists recognised the need to establish a system of internationally agreed measurement standards. Prior to this, various systems existed across the world and were merged and transformed through trade and acculturation.

The Egyptian Cubit

As measurements were sometimes formed from a natural basis, their accuracy was difficult to determine. The Egyptian cubit, an ancient unit based on the forearm length, ranged between 43 and 53 cm throughout antiquity and depended on the Pharaoh reigning. The Egyptian royal cubit is the earliest recognised standard of measurement.

The flood level of the Nile in approximately 3,000 B.C. was given as 6 cubits and 1 palm, and the royal cubit was a crucial measurement in ancient Egyptian architecture from as early as 2,700 B.C.

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The Roman Mile

Although the standardisation of the mile to 1.609 kilometres would not be established until an international agreement in 1959, the Roman mile of antiquity had consisted of a thousand paces of two steps each.

Armies marching through unchartered territories would drive sticks into the ground after each 1,000 paces, marking the length of the mile dependent on a variety of factors, including weather conditions, army logistics and the physical conditioning of soldiers.

Medieval Metrics

In medieval England, one form of measurement was used to calculate ounces of bullion and other tradable commodities, though its use was consistent with those recognised in both medieval Italian texts and ancient Athenian ones.

The inconsistencies, as well as regional and cultural differences of systems of measurement, prevented any universal application of a single standard of metrology. Without an effective means for the exchange and distribution of knowledge in the ancient and medieval worlds, it would be impossible for scientists, mathematicians, chemists and physicists to cooperate in the pursuit of progressive endeavours.

It would not be until the Scientific Revolution during the early modern period that metrology would cease from being utilised largely for the measurements of length, time and weight. As science advanced, a coherent system of units was required.

The discovery and identification of fundamental scientific principles such as electricity, atoms and thermodynamics allowed them to be applied to standards of measurement, thus facilitating the quantitative and qualitative assessment of physical properties in science.  

The Role of Microscopy

Microscopy, one of the earliest methods of particle sizing, dates to 1590 when two Dutch spectacle makers, Hans and Zaccharias Janssen, developed the first compound microscope.

Though initially used as a tool of identification, the development of high-precision lenses, digital image capture, and high-speed computers, have given rise to a stratospheric leap in the capability of the microscope in the present day.

Microscopes are unique as they are able to describe a particle’s shape, which permits scientists a better understanding of not only constituent particles but also the behaviour of groups of particles.

World's Roundest Object: Veritasium/YouTube

Defining the Metre

Even in the eighteenth century, unified systems of measurement did not exist even on a national level. France, a centre of science and enlightenment during the Scientific Revolution, recorded in 1795 that there were over 700 different units of measurement in the country.

In 1791 a commission had been established to decide between three possible references of measurement:

  • the length of a pendulum beating at a rate of one second at a latitude of 45ᵒ
  • the length of one quarter of the equator
  • the distance from the North Pole to the equator (a quarter meridian)

The distance from the North Pole to the equator was chosen as the simplest reference of measurement to calculate. In the same year, the metre was defined as being equal to the ten millionth part of one quarter of the terrestrial medium.

The metre materialised the concept of a “unit which in its determination was neither arbitrary nor related to any particular nation on the globe.”

The length of the meridian had to be identified and the triangulation work carried out by Jean-Baptiste Joseph Delambre and Pierre-Francois Meçhain took 7 years to complete. It was recognised to be equivalent to 10 million metres.

The Decimal Metric System

With the recognition of one base unit of measurement, others had to be established. The decimal metric system was introduced in 1795 by a weights and measures law, and by 1799 the system had extended to encompass the first standards of the metre and kilogram for everyday use.

The decimal metric system, as a simple, accessible and universal method, began to spread outside of France during the early 19th century. The metric system was mandatory in the Netherlands from 1816 and was adopted by Spain in 1849.

The Industrial Revolution

The emergence of the Industrial Revolution depended on the adoption of accurate units of measurement, as mass production, equipment commonality and assembly lines would be impossible without one.

In a typical act of Anglo-Franco rivalry, the British imperial system of units was adopted in the Weights and Measures Act of 1824, and it was retained until the UK joined the European Economic Community in the 1970s. Some imperial measurements are still in use, such as the pint which is still a popular measure of volume today in British pubs.

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The Système International d'Unités (SI Units)

In 1960, the Système International d'Unités (SI) was adopted to ensure a practical system of measurement. It established the use of seven SI base units:

  • metres (m) - a measure of length
  • ​kilograms (kg) - a measure of mass
  • seconds (s) - a measure of time
  • amperes (A) - a measure of electric current
  • kelvins (K) - a measure of thermodynamic temperature
  • ​moles (mol) - a measure of the amount of substance
  • candelas (cd) - a measure of luminous intensity

Such developments have emerged due to the growing need in the 20th and 21st centuries to ensure an open, transparent and comprehensive system of metrology that would provide the technical basis for wider agreements negotiated in science, trade, commerce, and regulatory affairs.

Initially, metrology emerged as a scientific system of calculation from a natural basis to pre-empt the subsistence needs of growing populations. Since antiquity, it has progressed to become to a universal language within science, industry and commerce, to permit the continuing enlightenment and advancement of humankind, as well as the distribution of knowledge and resources across the international stage.

New Metrology

The National Physics Laboratory (NPL) is the UK's National Measurement Institute which specialises in understanding metrology and helping people reduce uncertainty of measurements. The NPL believes that metrology for the 2020s needs to develop to be useful to society in the 2020s. It is focusing on four elements including:

  • The Quantum SI - As a result of a new quantum SI, several of the base units of measurement need to be revised and redefined to remove any remaining physical artefacts. The will allow for taking advantage of the advances in quantum metrology.
  • Measurement at the frontiers - Advances in science and technology are pushing the frontiers of what is possible for metrology.  
  • Embedded and ubiquitous measurement - Metrology capability will be embedded at the heart of products and systems in an example of technological convergence.
  • Smart and interconnected measurement - Large-scale, multi-measurement systems will exploit the availability of networked information to be able to make use of the 'internet of things', where physical objects integrate into the global information network.

Sources and Further Reading

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