ELECTRICAL STANDARDS 185 



document of fundamental importance. It was 

 written by Clerk Maxwell and Fleeming Jenkin. 

 Weber had shown that there were two practical 

 systems possible, the one based on the attraction 

 between two small bodies electrically charged, the 

 other on Orsted's discovery of the action between 

 a current and a magnetic pole. Faraday and Joule 

 had laid the necessary foundations for the work of 

 the committee ; Faraday by his discovery of the laws 

 of electro-magnetic induction and of electrolytic 

 action, Joule by his work connecting the strength 

 of a current with the heat it produces in a conductor 

 which it traverses, and hence with the energy to 

 which that heat is equivalent. The application of 

 this leading to a definition of electromotive force in 

 terms of energy is due to Thomson. 



These relations when clearly stated lead to 

 definitions of the various electrical quantities ; the 

 next step was to translate these definitions into stan- 

 dards of measurement which could be used in trade 

 and manufacture, and thus put the rapidly growing 

 electrical industry on a sound scientific basis. 



This work the committee undertook. The 

 fundamental quantities to be measured are electro- 

 motive force and current ; the ratio of these is 

 known as electrical resistance, and, as resistances are 

 compared more readily than electromotive forces, 

 resistance and current were chosen as fundamental 

 units. Maxwell, Fleeming Jenkin, and Balfour 

 Stewart undertook to realise the unit of resistance 

 to which was given the name ohm ; the work was 

 carried out in 1863, and is described in Appendix D 

 to the Report of that year. 



Standards representing the ohm were constructed 



