Invention of the Infinitesemal Calculus by Newton and Leibniz and its applications in Physics.
Reading: (1) Leibniz, A New Method of Maxima and Minima; On a Deeply Hidden Geometry; (2) Newton, Quadratura of Curves (all in D.J. Sruik (ed.), A Source Book in Mathematics 1200-1800, p. 271 ff)