A conception bearing the same relation to an electric current that lines
of force do to a field of force; elementary currents. If evenly
distributed the current is of uniform density; if unevenly distributed,
as in alternating currents, the current density varies in different
parts of the cross section of the conductor. This evenness or unevenness
may be referred to the number of streamlets per unit of area of
cross-section.

[Transcriber's note: Streamlets per unit of area is redundant with
current density.]