International System of Electrical and Magnetic Units
The International System of Electrical and Magnetic Units is an obsolete system of units used solely for measuring electrical and magnetic quantities. It was introduced by the Fourth International Conference of Electricians (Chicago, 1893) and modified in 1908. It was rendered obsolete by the inclusion of electromagnetic units in the International System of Units (SI) in 1948.
1893 system
The International System was introduced in 1893 because of the practical difficulties in measuring electrical units in the cgs system. The 1893 system had three base units: the international ampere, the international ohm and the international volt.
| Unit | 1893 ("international") definition | cgs ("absolute") equivalent | Notes |
|---|---|---|---|
| Ampere | the unvarying electric current that will deposit 0.001 118 000 grams of silver per second from a solution of silver nitrate in water | the current produced in a conductor with a 1 ohm resistance when there is a potential difference of 1 volt between its ends | |
| Ohm | the electric resistance of a column of mercury of constant cross-section at the temperature of melting ice, 106.3 centimetres long and with a mass of 14.4521 grams | equal to 109 cgs units of electric resistance | |
| Volt | such that the electromotive force of a Clark cell at a temperature of 15 °C is exactly 1.434 international volts | the electromotive force produced in an electric circuit which cuts 108 magnetic lines of force per second | equal to 108 cgs units of electromotive force |
Overdefinition and the 1908 modification
References
External links
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