The dirac delta function has solid roots in 19th century work in 19th century work in fourieranalysis and singular integrals by cauchy and others, anticipating dirac sdiscovery by over a century, and illuminating the nature of cauchy sinfinitesimals and his infinitesimal definition of delta.the dirac delta function has solid roots in 19th century work in 19th century work in fourieranalysis and singular integrals by cauchy and others, anticipating dirac sdiscovery by over a century, and illuminating the nature of cauchy sinfinitesimals and his infinitesimal definition of delta.