The Paris Congress Units (1884) are now universally adopted and consist
as follows:
_Electro-motive Force, and Potential_ (E).—The Volt. _The legal volt
is ·926 of the E. M. F. of a Daniell’s cell, which for rough purposes
may be taken as a volt._
_Resistance_ (R).—The Ohm. The legal ohm is now represented by the
resistance of a column of mercury of a square millimetre in section at
the temperature of zero centigrade 1·062 metres long.
_Current_ (C).—The Ampère. This is the strength of current sent
through a wire having the resistance of 1 ohm at the E. M. F. of 1 volt.
_Quantity_ (Q).—The Coulomb. It is the quantity of electricity given
by an ampère in a second. One coulomb decomposes ·00142 grain of water.
_Heat or Work_ (W).—The Joule, or Volt-Coulomb, is the work done by 1
coulomb in 1 ohm. The work done by any current per second is obtained
in ergs by the product of the current into the electro-motive force
producing it or W = CE or W = C²R. The Erg is the C. G. S. unit of
work.
_Power_ (P).—The Watt, 1 ÷ 746 of a horse-power, employed in doing 1
joule of work in 1 second.
HP, or the Horse-power, is found by dividing C E by 746, thus (CE)/746
or (C²R)/746 = HP.
See also explanation of terms.