absolute system

electromagnetics (Metric) The evolution of telecommunications and other applications of electricity in the 19th century led to a plethora of units for associated measurement. Concomitant realization that the electrical and magnetic effects could be represented in mechanical terms led to the expression of electromotive force and current, and thereby resistance, in terms of the metre, gram, and second. Such expression of the electrical in terms purely of the established mechanical units was called ‘absolute’.

Gauss is seen as pioneering this absolutism, within the context of his millimetre-milligram-second system,
[Nature Vol. 62, 414 (1900)] but it became significant only in the context of the c.g.s. system. The first such unit was the BA unit defined by the British Association in 1861 for resistance, computed but then enshrined as a wire; which to be realistic was set at 10⁷ times the fully coherent theoretical value within the natural m.g.s. system. Subsequently the Association accepted that the c.g.s. system was preferable to the m.g.s. system, producing units that gave more comparable readings in a given circumstance; it also accepted the name ohm for the previously established unit.

The first International Electrical Conference of 1881 made both of these accepted systems international, and moved to establish a fuller system. This system was to be ‘practical’, i.e. with units of the size that occurred in normal work. Its basis was the absolute c.g.s. units, which became the abohm, abvolt, etc., of the e.m.u. system. Its scaling would be of the order of the BA unit, and had to provide units that were mutually coherent. Termed pedantically the absolute practical system, the units became familiarly known as the practical units.