A practical unit of inductance introduced in 1887¹ in Great Britain and mainly used by the British, even after the International Electrical Congress (Paris, 1889) had adopted the term quadrant.² The secohm is equal to the product of the second and the legal ohm, and is approximately equal to the henry.

1. W. E. Ayrton and J. Perry.
Journal of the Society of Telegraphic and Electrical Engineers (), volume 16, page 320. (1887)

2. L'Electricien, August 9, 1890. Page 750.



The name proposed by Ayrton and Perry for the commercial electromagnetic unit of self-induction in a coil or circuit, or of mutual induction between two coils = 1 second × 1 legal ohm, or 1 legal ohm second. It bears the same numerical relation to the absolute C.G.S. unit of induction as the legal ohm bears to the absolute C.G.S. unit of resistance, probably about .9972 to 1.

Latimer Clark.
A Dictionary of Metric and Other Useful Measures.
London: E & F.N. Spon, 1891.
Page 83.


The henry has been known also by the names “quadrant” and “secohm.” Both names are based on dimensional considerations. … The name “secohm” is a combination of second and ohm, inductance having the same dimensions as time multiplied by resistance, and this unit fitting into the same system as the ohm and the second.

[U.S.] Department of Commerce.
Circular of the Bureau of Standards No. 60.
Electric Units and Standards.
Washington: U.S.G.P.O., 1916.
Page 45.

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