unit of resistance

A unit of electric resistance, 19ᵗʰ century, equal to the resistance of a pure copper wire 1/16th of an inch in diameter and 1 statute mile long, at a temperature of 60°F. Fleeming Jenkin measured it as 13.59 B.A. ohms,¹ about 13.41 true ohms.

This unit is sometimes confused with Varley’s unit of resistance. The difference appears to be that this unit specifies pure annealed copper wire, while Varley's unit used standard copper telegraph wire. As a result Mathiessen’s unit is about half the resistance of Varley’s.

1. British Assn. for the Advancement of Science.
Reports of the Committee on Electrical Standards appointed by the British Assn. for the Advancement of Science...With a report to the Royal Society on units of electrical resistance, by Prof. F. Jenkin....
London: E. & F. N. Spon, 1873.
We provide Jenkin's report as a PDF file.



L'unité de Matthiessen, 1 mille anglais (1609m,34) de fil cuivre pur de 1/16 de pouce (0m,0016) de diamètre è 15°,5 C.

Matthiessen's unit, 1 English mile (1609.34 meters) of pure copper wire 1/16th of an inch in diameter at 15.5° centigrade.

H. Schoentjes.
Les Grandeurs èlectriques et leurs unités. 2nd ed. revised and augmented.
Paris: Librairie de Gauthier-Villars èditeur, 1884.
Page 102.


For an excellent history of the development of the electric and magnetic units up to 1913, see U. S. Bureau of Standards Circular 60.

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