1911 Encyclopædia Britannica/Commutation

COMMUTATION (from Lat. commutare, to change), a process of exchanging one thing for another, particularly of one method of payment for another, such as payment in money for payment in kind or by service, or of payment of a lump sum for periodical payments; for various kinds of such substitution see Annuity; Copyhold and Tithes. The word is also used similarly of the substitution of a lesser sentence on a criminal for a greater. In electrical engineering, the word is applied to the reversal of the course of an electric current, the contrivance for so doing being known as a “commutator” (see Dynamo). In America, a “commutation ticket” on a railway is one which allows a person to travel at a lower rate over a particular route for a certain time or for a certain number of times; the person holding such a ticket is known as a “commuter.”