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weber

engraving from a photograph of Weber

For the meaning of any metric prefix, go here.

1

The unit of magnetic flux in SI. Symbol, Wb (no period).

One weber is “the magnetic flux which, linking a circuit of one turn, would produce in it an electromotive force of 1 volt if it were reduced to zero at a uniform rate in 1 second.” (Resolution 2, CIPM, 1946, ratified by the CGPM in 1948.) The weber is volt seconds or, in terms of base units only,

$A fraction: meters squared times kilograms over seconds squared times amperes$

The weber was introduced as a practical electromagnetic unit = 10⁸ maxwells at the International Electrotechnical Commission in Paris in 1933, but it was not much used until the meter-kilogram-second system was generally adopted.

The weber is named for Wilhelm E. Weber (1804-1891).

sources

Taking into account the fact that the question of magnetic units is still under discussion by various bodies, the Committee wish to come to no hasty decisions, but they recommend for tentative adoption the following terminology:-

1. That, as a unit for magnetic field, a hundred million “C.G.S. lines” be called a weber.

Note.-A weber added per second at a steady rate to the field girdled by a wire circuit induces one volt in every turn of that circuit.

Hence the webers “cut” by a closed wire circuit of n turns are equal to the quantity of electricity in coulombs thereby impelled round that circuit multiplied by 1/n th its resistance in ohms.

Twenty-Second Report- Ipswich, 1895.
Reports of the Committee on Electrical Standards Appointed by the British Association for the Advancement of Science.
Cambridge: Cambridge Univ. Press, 1913.
Page 520.

2

In the 19ᵗʰ century, a unit of electric current, and sometimes a unit of quantity of electricity.

sources

Through many an ohm the weber flew,
And clicked the answer back to me,—
I am thy farad, staunch and true
Charged to a volt with love for thee.

James Clerk Maxwell.
“Valentine from a male telegraphist to a female telegraphist.”

Yes, the James Clerk Maxwell. This is merely the last verse of the poem. It is reproduced from Alexander MacFarlane, Lectures on Ten British Physicists of the Nineteenth Century.

A further question arising out of the mutual relations of the fundamental units was that of the magnitude of the practical units to which distinctive names should be attached. The present usage with respect to this matter is that a resistance of 10⁹ C. G. S. units is called an Ohm; an electromotive force of 10⁸ C. G. S. units is called a Volt; and the current produced by a Volt acting through an Ohm, that is to say, a current of 10⁸ ÷ 10⁹ or 0.1 C. G. S. unit is called a Weber. In the opinion of the Committee it was considered highly desirable, from a scientific point of view, that the relations among these standards should be simplified by defining them as follows:-

Ohm = 10⁹ C. G. s. units of resistance.

Volt = 10⁸ C. G. S. units of electromotive force.

Weber = 1 C. G. S. unit of current.

It was felt, however, that any recommendation involving a change in the value attached to terms which are rapidly coming into extensive use among practical electricians, might give rise to serious inconvenience. Therefore, although with regard to the scientific aspect of this proposal the Committee were decidedly in favour of the change, they felt that a public recommendation could not well be made until the practical inconveniences likely to follow had been very carefully investigated.

Eighth Report- York, 1881.
Reports of the Committee on Electrical Standards Appointed by the British Association for the Advancement of Science.
Cambridge: Cambridge Univ. Press, 1913.
Page 296.

L'unité pratique d'intensité porte le nom d'Ampère et est égale à 10⁻¹ unités C. G. S. (C'est l'ancien weber par seconde anglais.)

…

L'unité pratique de quantité porte le nom de Coulomb et est égale à 10⁻¹ unités C. G. S. (C'est l'ancien weber anglais.)

Édouard Hospitalier.
Formulaire Pratique de l'Electricien.
Paris: G. Masson, 1883.
Page 37. Édouard Hospitalier's work first appeared in 1883. It was extremely popular and went through 29 editions, the last in 1919.

The practical unit of current strength is called the ampère, and is equal to 10⁻¹ C. G. S. units. (It is the old Weber per second often called the Weber.)

…

The practical unit of quantity is called a coulomb, and is equal to 10⁻¹ C. G. S. units. (This is the old Weber.) [Italics are the author's.]

Gordon Wigner, translator.
The Electrician's Pocket-Book. The English Edition of Hospitalier's Formulaire Pratique de l'Electricien.
London: Cassell & Company, 1884.
Page 42. Notice that Hospitalier identifies this use of the weber as English, which Wigner's translation omits. The implication is that “weber” did not have these meanings on the continent.

WEBER. The name originally given to the unit of electric quantity or coulomb.
[Footnote] Weber or Veber also became commonly used to define the unit of electrical current—a contraction of “webers per second”— but was replaced by “ampere” at the Paris Congress of 1884. It was once proposed to designate the unit magnetic pole.

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

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