surname, later masc. proper name, attested from late 12c., from Maxwell, name of a town on the River Tweed on the Scottish borders (the name is probably "the well of Macc or Macca"). In physics, usually a reference to James Clerk Maxwell (1831-1879), as in Maxwell's demon (1879; as Maxwell's "intelligent demons" from 1874).
The definition of a "demon," according to the use of this word by Maxwell, is an intelligent being endowed with free will, and fine enough tactile and perceptive organisation to give him the faculty of observing and influencing individual molecules of matter. ["Nature," April 9, 1874]