FLUXIONS, a form of the calculus (q.v.) developed by Sir Isaac Newton (q.v.), beginning in 1663. The word fluxion, as used by him, denoted the rate at which a variable (flowing quan tity, fluent) increases or decreases at a given instant of time. If x and y were taken to be the flowing quantities (fluents) then it could be shown that In the alternative differential notation we should have (See CALCULUS.)