HEGEL’S KILOGRAM: ON THE MEASURE OF METRICAL UNITS In 1799, two rather unusual objects were deposited in a vault at the In- ternational Bureau of Weights and Measures (BIPM) in Sèvres, France: a platinum bar and a platinum cylinder that would serve as standard inter- national reference units for the meter and for the kilogram. How were the quantities and the qualities of these objects determined? In 1791, the meter was defined by the French Academy of Sciences as one ten millionth of the length of the earth’s meridian, passing through Paris between the North Pole and the Equator. The measurement of the meridian itself was carried out through a six year surveying project, from 1792-1798, determining the length of a portion of the meridian running from Dunkirk to Barcelona through a complex system of triangulation between observation points 1 . The kilogram was defined as the mass of a cubic decimeter of water at 4 degrees Celsius (the temperature of water’s maximum density). Once these measurements were taken and the reference objects fabricated and archived, the properties of the objects themselves then served to define the meter and the kilogram as units: by definition, a meter was equal to the length of the prototype in Sèvre; a kilogram was equal to the mass of the kilogramme des archives. These objects would serve as reference standards until 1889, when they were replaced with platinum-iridium alloy reference standards follow- ing the international adoption of the metric system. The initial determina- tion of these units and the creation of their first reference standards in the 1 For a concise account, see R. A. Nelson, Foundations of the International System of Units, «The Physics Teacher», XIX (1981), 9, pp. 596-613. For a narrative account, see Ken Adler’s classic, K. Adler, The Measure of All Things, New York, Free Press, 2002. See also H. A. Klein, The Science of Measurement: A Historical Survey, New York, Dover, 2011, pp. 105-119. «Azimuth», V (2017), nr. 10 © 2017 Edizioni di Storia e Letteratura - Inschibboleth http://storiaeletteratura.it/category/azimuth/ ISSN (paper): 2282-4863 ISBN (paper): 978-88-9359-110-2 ISBN (e-book): 978-88-9359-111-9