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Kelvin Electrical Balance


Creator: UoD_Museums on 18 Sep 2011, 3:55 p.m.

This instrument was made by the Glasgow company James White. Founded in 1850, the firm enjoyed a highly productive professional relationship with William Thomson (later Lord Kelvin), Professor of Natural Philosophy at the University of Glasgow. White supplied equipment for Thomson’s laboratory and later produced instruments to Thomson’s own designs. In 1900, Kelvin became a director in the newly amalgamated firm of Kelvin & James White Ltd. The company survives today as Kelvin Hughes Ltd, producing marine navigation systems.

Kelvin designed this form of current balance in 1887. It became commonly used in laboratories to standardise and calibrate equipment. The instrument has a moving coil at the end of each arm of the balance. Each moving coil is positioned between two fixed coils which ensures that the instrument is fully shielded from any errors caused by induced currents. The coils were wired such that an induced current in one set of coils cancelled out the current in the other.