Precise dimensions: a history of units from 1791–2018 (original) (raw)
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2008
Citation for the Trevor Evans Award: "In this outstanding article, Randy K. Schwartz gives a historical perspective of the development of the meter as a precise form of measurement beginning his account in the wake of the French Revolution. The birth of this unit of measurement was not without its pains. Amidst the political turmoil of the 1790s, a heated debate ensued from the decision to replace over 250,000 different weights and measures with a system of measurement that would not be arbitrary. The author verses readers in the mathematical arguments as to how a meter should be defined – as a unit related to the swing of a pendulum or proportional to the size of the Earth. Readers see how each idea was implemented in its turn and learn the mathematical challenges inherent in each. The author explains the motion of a pendulum clock and why it does not lead to the desired universal measurement. Readers also learn about the French surveying project, the complications associated with it, and its ultimate success. In each step of the article, readers are exposed to wonderful descriptions of how mathematical tools, ranging from trigonometry to differential equations, were used to define the meter."
Adapting the International System of Units to the twenty-first century
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2011
We review the proposal of the International Committee for Weights and Measures (Comité International des Poids et Mesures, CIPM), currently being considered by the General Conference on Weights and Measures (Conférences Générales des Poids et Mesures, CGPM), to revise the International System of Units (Le Système International d'Unitès, SI). The proposal includes new definitions for four of the seven base units of the SI, and a new form of words to present the definitions of all the units. The objective of the proposed changes is to adopt definitions referenced to constants of nature, taken in the widest sense, so that the definitions may be based on what are believed to be true invariants. In particular, whereas in the current SI the kilogram, ampere, kelvin and mole are linked to exact numerical values of the mass of the international prototype of the kilogram, the magnetic constant (permeability of vacuum), the triple-point temperature of water and the molar mass of carbon-12...
A milestone in the further development of the International System of Units
2018
The General Conference on Weights and Measures is expected to adopt a fundamental revision of the International System of Units (SI) on the 16th of November 2018. Newly, a set of seven defining constants with fixed values completely sets the system and forms the basis for defining the units. After more than one hundred years of use, the revision will release the last artifact in the SI, the prototype kilogram, from service and replace it with a mass unit based on natural constants.