What is "angle of commutation"

Commutation \Com`mu*ta"tion\, n. [L. commutatio: cf. F. commutation.]

1. A passing from one state to another; change; alteration; mutation. [R.]

   So great is the commutation that the soul then hated only that which now only it loves.
   --South.

2. The act of giving one thing for another; barter; exchange.

   The use of money is . . . that of saving the commutation of more bulky commodities.
   --Arbuthnot.

3. (Law) The change of a penalty or punishment by the pardoning power of the State; as, the commutation of a sentence of death to banishment or imprisonment.

   Suits are allowable in the spiritual courts for money agreed to be given as a commutation for penance.
   --Blackstone.

4. A substitution, as of a less thing for a greater, esp. a substitution of one form of payment for another, or one payment for many, or a specific sum of money for conditional payments or allowances; as, commutation of tithes; commutation of fares; commutation of copyright; commutation of rations.

5. regular travel from a place of residence to a place where one's daily work is performed; commuting. Most often, such travel is performed between a suburb and a nearby city.

   Angle of commutation (Astron.), the difference of the geocentric longitudes of the sun and a planet.

   Commutation of tithes, the substitution of a regular payment, chargeable to the land, for the annual tithes in kind.

   Commutation ticket, a ticket, as for transportation, which is the evidence of a contract for service at a reduced rate. See 2d Commute, 2.