The International System of Units: SI

Abstract

Unity of measurements is understood as consistency on the dimensions of the units of all quantities. This is evident when recalling the possibility of measuring one and the same quantity by direct and indirect measurements. Such consistency is achieved by the creation of a system of units. But, although the advantages of a system of units were recognized long ago, the first system of units appeared only at the end of the eighteenth century. This was the celebrated metric system (meter, kilogram, second), authorized March 26, 1791 by the Constituent Assembly of France. The first scientifically based system of units, as a set of arbitrary base units and dependent units derived from them, was presented in 1832 by Carl Gauss. He constructed a system of units, called absolute units, at the base of which were three arbitrary and mutually independent units: millimeter, milligram, and second. A further development of Gauss’ system was the CGS system (centimeter, gram, second) that appeared in 1881 and was convenient for use in electromagnetic measurements, as well as various modifications to it.