Wilhelm Eduard Weber died in 1891, yet his name became the standard for measuring the invisible force that powers the modern world. The weber is the SI derived unit of magnetic flux, a concept that describes the total magnetic field passing through a given area. Without this unit, the relationship between electricity and magnetism would remain a collection of abstract equations rather than a practical tool for engineering. A magnetic flux density of one weber per square meter defines the tesla, the unit used to measure the strength of magnetic fields in everything from MRI machines to particle accelerators. The weber itself is defined through Faraday's law of induction, which states that a change in flux of one weber per second will induce an electromotive force of one volt. This simple relationship allows engineers to calculate how much electricity can be generated by moving a magnet through a coil of wire, forming the basis of all electric generators.
A Century of Naming
The history of the weber began in 1861 when the British Association for the Advancement of Science established a committee under William Thomson to study electrical units. For decades, the naming of these units was a chaotic patchwork of different systems used by different countries and scientists. In 1902, Giovanni Giorgi proposed a set of rational units of electromagnetism that included the weber, noting in a manuscript with handwritten notes from Oliver Heaviside that the product of the volt into the second had been called the weber by the British Association. The International Electrotechnical Commission began work on standardizing terminology in 1909 and established Technical Committee 1 in 1911 to sanction the terms and definitions used in electrotechnical fields. By 1930, the committee decided that the magnetic field strength was of a different nature from the magnetic flux density, but they delayed naming the units until general agreement could be reached on their definitions. It was not until 1935 that Technical Committee 1 recommended names for several electrical units, including the weber for the practical unit of magnetic flux and the maxwell for the CGS unit.The Giorgi System
The true unification of electromagnetic units occurred through the work of Giovanni Giorgi, who proposed a system that linked mechanical units with electrical ones. In 1935, Technical Committee 1 passed responsibility for electric and magnetic magnitudes and units to the new Technical Committee 24. This committee eventually led to the universal adoption of the Giorgi system, which unified electromagnetic units with the MKS dimensional system of units, creating what is now known as the SI system. In 1938, Technical Committee 24 recommended the permeability of free space as a connecting link from mechanical to electrical units. The group recognized that any one of the practical units already in use, such as the ohm, ampere, volt, henry, farad, coulomb, or weber, could equally serve as the fourth fundamental unit. After consultation, the ampere was adopted as the fourth unit of the Giorgi system in Paris in 1950, cementing the weber's place in the international standard.