Natural Philosophy Collection

Kelvin Current Balance

In the 1880s, the electric power industry began to make its presence felt in earnest. Dynamos could be built large enough to provide for the electric lighting throughout a factory or to power a tramcar system or small electric railway. In proportion to the spread of electrical installations, there was a need for electric meters. For high precision measurements, constituting an effective local standard, one family of meters became very widely used. William Thomson, Professor of Natural Philosophy at Glasgow, who was created Baron Kelvin of Largs in 1892, invented them. They worked on fundamental principles and were cleverly designed so that effects which might cause an error were largely balanced out. The constancy of their calibration relied only on the constancy of a set of weights. Our centi-amp balance, no 61, shown with its cover removed and complete with box of ancillaries, is in excellent unrestored condition. It was made circa 1890 by the firm of instrument makers with whom Thomson developed the details of many instruments he designed: James White of Glasgow.

John S. Reid