The impedance analogy is sometimes called the Maxwell analogy[29] after James Clerk Maxwell (1831–1879) who used mechanical analogies to explain his ideas of electromagnetic fields.[30] However, the term impedance was not coined until 1886 (by Oliver Heaviside),[31] the idea of complex impedance was introduced by Arthur E. Kennelly in 1893, and the concept of impedance was not extended into the mechanical domain until 1920 by Kennelly and Arthur Gordon Webster.[32]