(The delta function revisited: from Heaviside to Dirac)

The delta ($\delta$) function, named after the English physicist Paul Adrien Maurice Dirac ($\star$ 1902, †1984) in a 1927 pioneer work, became a fundamental tool to modern science and engineering, with applications covering areas from quantum theory to industrial process control. It facilitates the obtention of countless results that, in other ways, would require complicated arguments. Nonetheless, its definitions in literature are, frequently, presented with few or no meaning, even though they had been correctly applied in the solution of several problems. This paper intends to show the ingenious and inventive way of development of this extraordinary tool that, besides Dirac, had the contribution of others, such as the french mathematician Laurent Moise Schwartz ($\star$ 1915, †2002), with the theory of distributions, as well as the eccentric and self-taught English mathematical physicist called Oliver Heaviside ($\star$ 1850, †1925).

Keywords:
impulse function; Dirac's delta; history of physics; history of electrical engineering; theory of distributions