A system of units proposed in 1940 by G. E. M. Jauncey and A. S. Langsdorf, formed by adding the ohm to the M.K.S. system. The reason for the choice of the ohm as the fourth fundamental unit is best described by the proposers themselves:
The problem now is to decide which electric or magnetic unit shall be chosen as the fourth fundamental unit. The practical electric units–the ampere, volt, etc.–are more commonly used than the magnetic units–the oersted, gilbert, etc.–and so our choice is limited to the ampere, volt, ohm, coulomb, farad and henry.
As pointed out in Chapter I, it is desirable in selecting a set of fundamental units that each standard be of such character that it can be deposited in a suitable place for safe keeping, and that, no matter what may have been the original specifications for the standard, the standard when once deposited should from then on become the accepted unit. Since it is difficult to think of a coulomb, ampere, or volt being deposited at Sèvres, France, or at the United States Bureau of Standards, our choice is limited to the ohm, farad, and henry; and of these three we definitely favor the ohm because when embodied in a resistor it is less destructible and less liable to change than either of the others. A mechanical shock could easily change the inductance of an inductor or the capacitance of a capacitor.
G. E. M. Jauncey and A. S. Langsdorf.
M. K. S. Units and Dimensions and a Proposed M. K. O. S. System.
New York: Macmillan, 1940.
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Last revised: 11 July 2001.