 Newton later became discontented with the undeniable presence of infinitesimals in his calculus, and dissatisfied with the dubious procedure of “neglecting” them. In the preface to the De quadratura curvarum he remarks that there is no necessity to introduce into the method of fluxions any argument about infinitely small quantities. In their place he proposes to employ what he calls the method of prime and ultimate ratio. This method, in many respects an anticipation of the limit concept, receives a number of allusions in Newton’s celebrated Principia mathematica philosophiae naturalis of 1687.