Chronological History of the Metric System

Four distinct aims came to a focus in the metric system:

  1. Standardization of a national metrology in France.
  2. Use of a natural standard of length.
  3. Use of a decimal scale.
  4. An international system of weights and measures.

It is the international aspect of the metric system that is its present chief claim to importance; but the need for uniform weights and measures throughout France was the essential condition that made initial action possible there. The proposal to adopt a natural standard of length endowed the scheme with a sufficiently scientific aspect to attract outside attention and some co-operation; which paved the way for the subsequent acts of practical standardization that are the real foundation of its international Success.

The decimal scale, which makes the metric system so convenient for some calculations, probably was the least important of the political factors: perhaps the revolutionary spirit was the chief accelerator of legislation, but the public at large would not be hustled. The metric system became the legal metrology of France in the third year of the Republic (1795); but, seventeen years later, Napoleon found popular disregard of it to be so prevalent that he sanctioned a parallel system in which the old names and customary fractions were applied to the new units. It was not until 1837 that his decree was repealed; and the use of other than the decimal metric measures became a penal offence. By that time, a new generation had been taught at school (also by Napoleon's decree) to become familiar with the new system.

In the century before the metric system was adopted there had been several advocates of a new universal metrology based on a natural unit of length: for example:

Knowing that Sir John Riggs Miller, in the House of Commons during 1789, had raised the question of weights and measures, Talleyrand wrote this private letter to him on 29th March 1790.


I understand that you have submitted for the consideration of the British Parliament, a valuable plan for the equalization of measures: I have felt it my duty to make a like proposition to our National Assembly. It appears to me worthy of the present epoch that the two Nations should unite in their endeavour to establish an invariable measure and that they should address themselves to Nature for this important discovery.

If you and I think alike on this subject, and that you axe of opinion that much general benefit may be derived from it, it is through you only that we can hope for its accomplishment; and I beg to recommend it to your consideration. Too long have Great Britain and France been at variance with each other, for empty honour or for guilty interests. It is time that two free Nations should unite their exertions for the promotion of a discovery that must be useful to mankind.

I have the honour to be, Sir, with due respect, your most humble and obedient servant,

The Bishop of Autun (Miller's translation)

In the next session of Parliament Miller reported the receipt of this letter, and expressed himself in favour of the scheme; but nothing came of it. A few months later the bishop sent Miller a copy of the National Assembly's minute of 8 May, in which Louis XVI is asked to write to George III inviting joint action to determine a natural standard of weight and measure: but the Registrar found no such letter in the Royal Archives at Windsor Castle.

Second report by the committee recommending that the standard of length should be:
One ten-millionth of the meridian quadrant.

This length was to be determined by calculations based on the measurement of a meridian arc extending from Dunkirk to Barcelona; that is an extension of the line measured by Lacaille and Cassini in 1739. The decimal aspect of the system, recommended in their first report, was emphasized by discarding the traditional degrees and minutes of angular measurement. The committee rejected the pendulum, on principle, because it involved time as a non-linear element. The Academy of Sciences adopted the committee's recommendations.

Third report of the committee; recommending the name "metre" for the new linear unit, and giving its length provisionally as 443·44 lines. This provisional length was calculated from Lacaille's measurement; which showed the length of the meridian degree at latitude 45° to be 57027 toises.

Meridian quadrant = 57027 X 90 = 5132430 toises
= 5132430 x 864 = 443·44 X 107 lines

The Academy submitted its committee Is report to the Convention, which had replaced the National Assembly: this report was adopted by decree on 1st August, and a brass standard of the provisional metre was made: it is preserved in the Conservatoire des Arts et Métiers at Paris.

War with England began in this year.

Three platinum standards and several iron standards of the metre were now made.

The sub-committee, charged with the responsibility of making a standard of mass to represent a cubic decimetre of distilled water at the temperature of melting ice, also completed its work this year; and a platinum kilogram was constructed equal to 18827·15 French grains in the scale of the Pile de Charlemagne. In this scale the livre poids-de-marc was rated 9216 French grains: the mass of the kilogram, therefore, was equivalent to (18827/9216) = 2·0421 livres, and the mass of the livre was 489·69 gm.

Pat Naughton has pointed out that our source makes no mention of Bishop John Wilkins, who brought together the elements that became the Metric System when he invented the idea of a universal measure in 1668. See his page with details of the history of the development of his ideas at Wilkins

Other references on the web: