integral sign (original) (raw)

The integral sign

is a stylised version of the long s letter.

The long s is a typographic variant of lowercase s, being the only lowercase s in the Carolingian minuscule script. The modern short (round) s appeared later to the ends of words, and has now replaced completely the long s in the antiqua script.

Gottfried Wilhelm Leibniz introduced the integral sign as the first letter s of the Latin word summa (‘sum’). The long shape of ∫ may be thought to symbolically depict the fact that http://planetmath.org/DefiniteIntegralintegral is a limiting case of sum.

The function given after the integral sign, i.e. the function to be integrated, is the integrand.