These three units—ampere, volt, and ohm—are the factors in Ohm’s famous law that the current is directly proportional to the electro-motive force exerted in a circuit, and inversely proportional to the resistance of the circuit; that is,—
Current = Electro-motive force / Resistance
Electro-motive force = Current × Resistance
Resistance = Electro-motive force / Current.
ERG:—From the Greek _ergon_, work, is the unit of work required to move a force of one dyne one centimetre. One foot-pound equals 13,560 ergs.
CALORIE:—Latin _calor_, heat, is the unit of heat; being the amount of heat required to raise the temperature of one kilogram of water one degree centigrade.
COULOMB:—In honor of C. A. de Coulomb, of France. It is the practical unit of quantity in measuring electricity, and is the amount conveyed by one ampere in one second.
FARAD:—From FARADAY, the physicist. It is the unit of electric capacity, and is the capacity of a condenser that retains one coulomb of charge with one volt difference of potential.
GAUSS:—From Carl F. Gauss (1785–1855). The C. G. S. unit of flux-density, or the unit by which the intensity of magnetic fields are measured. It equals one weber per normal square centimetre.
GILBERT:—The unit for measuring magneto-motive force, being produced by .7958 ampere-turn approximately.
HENRY:—From Joseph Henry, of the Smithsonian Institution, Washington, D. C. The practical unit for measuring the induction in a circuit when the electro-motive force induced is one international volt, while the inducing current varies at the rate of one ampere per second.
JOULE:—The C. G. S. unit of practical energy, being equivalent to the work done in keeping up for one second a current of one ampere against a resistance of one ohm. Named from J. P. Joule, of England.
OERSTED:—From Oersted, the electrician. It is the practical unit for measuring electrical reluctance.
WATT:—The practical electrical unit of the rate of working in a circuit, when the electro-motive force is one volt, and the intensity of current is one ampere. It is equal to 107 ergs per second, or .00134 horse-power per second. Named from James Watt, of Scotland.
WEBER:—The practical unit for measuring magnetic flux. Named from W. Weber, of Germany.