Collier's New Encyclopedia (1921)/Integral Calculus
INTEGRAL CALCULUS, a branch of mathematics, the converse of the differential calculus. Having a given or known differential, the integral calculus has for its object to find a function such that, being differentiated, it will produce the given differential. Such expression is called the integral of the differential. The operation of finding the primitive function or integral is called integration. Besides the method of finding the integrals of given differentials, the integral calculus is also applied to various branches of mathematics, as well as to almost every branch of natural philosophy and engineering.