# 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 It was not until 1837 that his decree was repealed; and the use of other than the decimal metric measures became a penal offence.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:

• 1670. Gabriel Mouton, a scientist in holy orders at Lyons, proposed a linear scale based on a geodetic minute of are decimally divided. 1671. Picard suggested a 'universal foot,' represented by one-third of the length of a pendulum beating seconds.
• 1720. Cassini proposed the adoption of a geodetic foot representing (1/6000) terrestrial minute of arc. In 1740 he made geodetic measurements that established the length of that foot, and if it had been adopted at that time its equality with the Greek foot might have been recognized by Stuart when he measured the Parthenon soon after 1750. Cassini's measurements formed the basis of the provisional metre established in 1793, but this new decimal metrology drew a veil over the sexagesimal unit and it was not until 1812 that the geodetic appearance of the Greek linear scale was noticed by Jornard. This reference to it, however, failed to attract general attention or further inquiry.
• 1735-7. La Condamine, Godin, and Bouguer measured a geodetic arc of meridian, and found the length of the seconds pendulum at the equator to be 439·15 lines. These measurements were made in Peru, with a toise that became known as the Toise of Peru.
• 1739-40. Lacaille and Cassini measured an arc of meridian in Europe: the objective was to measure a line extending both sides of latitude 45° and the chosen meridian was that of Dunkirk-Barcelona. These measurements showed the length of the meridian degree at latitude 45° to be 57027 toises. Also, the length of the seconds pendulum at Paris was established as 440·5597 lines.
• 1747. La Condamine proposed that the length of the equatorial seconds pendulum should be adopted as a universal standard.
• 1778. Necker reported to Louis XVI that he had examined the means that might be employed to render the weights and measures uniform throughout the kingdom, but doubted whether the result would be proportionate to the difficulties involved.
• 1790. Talleyrand (then Bishop of Autun) submitted to the National Assembly a proposal to standardize the length of the seconds pendulum at 45° latitude. His proposal, having been referred to the Committee on Agriculture and Commerce, was recommended to the king, who sanctioned action on 22nd August. The French Academy of Sciences was made responsible, and appointed a committee that included Lagrange and Laplace among its members: their first report, in October, recommended the decimal division of money, weights, and measures.

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.

SIR,

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.

• 1792. French Republic established on 22 September, the day of the autumnal equinox. Mechain and Delambre began work on the meridian measurement.
• 1793. Louis XVI executed, on 21 January.

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.

• 1794. Execution of Robespierre, and end of the Terror.
• 1795. The metric system became the legal metrology of France by the Law of 7 April 1795. The franc was introduced into the coinage by this law.
• 1798. Mechain and Delambre having (with great difficulty, owing to the political conditions) established the difference in latitude between Dunkirk and Barcelona as 9° 39′, and allowed for the flattening of the earth, calculated the length of the meridian quadrant to be 5130740 toises. This was only 1 part in 3000 less than the calculated length based on Lacaille's measurement of a degree, and reduced the length of the provisional metre by only 0·46 line to:
Final metre = 5130740 x 864/107 = 443·296 lines .*. French foot (= 144 lines) = 0·24839 metre

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.

• Battle of the Nile. 1799. The new standards were presented formally to the Corps Lˇgislatif, and legalized by statute abolishing the provisional standards. One of the three new standard metres became known as the Metre of the Archives. The Government had intended to make a distribution of copies of the new standards but found the cost too high. For those in possession of copies of the Toise of Peru, the metre was represented by (443·296/864) of its length.
• 1800. A decree authorizing the use of a more popular nomenclature was issued.
• 1812. Public prejudice against the new scheme being still very strong, a parallel system was established in which the old names and customary fractions were applied to the new units: thus, the length of 2 metres was called a toise and divided into 6 pieds that were (1/3) metre in length. At the same time, a decree enacted that the legal decimal system must be taught in schools and used in all official transactions.
• Retreat from Moscow.
• 1837. The decree of 1812 was repealed, and it was enacted that the use of measures and weights other than those of the metric system would become a penal offence from the beginning of 1840.
• 1864. In England, Parliament passed an Act (27 and 28 Victoria, c. 117) legalizing the use of metric metrology in contracts; and providing a schedule of authorized equivalents: but this Act did not legalize the use of actual metric weights in trade. The authorized equivalents included:
1 metre= 39·708 in. 1 kgm. = 15432·3487 grains
1 are = =9·6033 sq. yds. 1 litre = 1·76077 pints
• 1867. A convention of the International Geodetic Association recommended the international use of the metric system in geodetic work, and advocated the construction of a new European prototype metre (differing as little as possible from the Mètre des Archives) to be available for international use, under the supervision of an international bureau.
• 1870. Franco-Prussian war.
• 1872. An International Commission, convened by the French Government, met at Paris and advocated the construction of international metric standards, to be kept by an international bureau located at Paris.
• 1875. The Metric Convention. Eighteen countries signed a treaty to establish and maintain an international bureau of weights and measures. England was not one of these signatories: the Warden of the Standards was a delegate to the 1872 Commission, but was not allowed to participate in subsequent events because 'Her Majesty's Government declared that they could not recommend to Parliament any expenditure connected with the metric system, which is not legalized in this country, nor in support of a permanent institution established in a foreign country for its encouragement. They have consequently declined to take part in the Convention or to contribute to the expenses of the new Metric Bureau, and have directed the Warden of the Standards to decline being appointed a member of the new International Committee or to take part in the direction of the new International Metric Bureau.' [On the Science of Weighing and Measuring, by H. W. Chisholm (Warden of the Standards), 1877].
• 1884. Great Britain joined the Metric Convention.
• 1897. 60 and 61 Victoria, c. 46. 'An Act to legalize the use of weights and measures of the metric system.' This Act permits the use of metric weights and measures in trade, and requires the Board of Trade to include metric denominations among its standards.

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:

DunkirkBarcelona1
DunkirkBarcelona2
DunkirkBarcelona3