Measuring rod no. 11, known as "the Measuring Rod of the Dépôt de la Guerre"
Measuring rod no. 11 of the Dépôt de la Guerre is a cast-iron measuring rod that was made by Baumann in Berlin sometime prior to 1852.
Like the metre, the “toise de France” (literal translation: French fathom) is a theoretical unit of length. It is calculated in relation to the dimensions of the Earth. The “toise” is derived from a measurement of the length of the Paris meridian, which was taken by Cassini in 1718.
The length of an arc of 1 degree of the meridian of Paris is equivalent to 20 French miles. And since there are 2000 “toises” in a French mile, the “toise” represents one 40 000th of this arc.
Up until the 19th century, this unit of length was given concrete form in a monumental display with a universal legal validity. The same applies for the metre, which is preserved in the pavilion of Breteuil near Paris.
This measuring rod is a copy of the measuring rod used at the Königsberg Observatory, which in turn is an exact copy of the original measuring rod which is known as the “Toise du Pérou” and was made in Paris in 1735. In 1852, it was compared to the Königsberg measuring rod in order to determine the exact length, which is 836.99901 lines.
In 1847, the chief of staff of the Prussian army lent us Bessel’s standard and their measuring rod no. 9 in order to measure the length of wooden rulers at two fathoms, which were intended for use in taking measurements for the geodetic bases in Belgium. Two bases were measured with these rulers, in Ostend and Lommel, in order to draw up the map of Belgium.
At the recommendation of the International Association for Geodetics, in 1898, measuring rod no.11 was sent to the Bureau international des Poids et Mesures in Breteuil for comparison with the metre. The comparison could only be made in 1913.
The length of the measuring rod was established at 1 949,06 millimetres, at 16°25.
This comparison was published in 1922 in the Bulletin de la Classe des sciences of the Royal Belgian Academy of Sciences.
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