15. Carl Friedrich Gauss (1777-1855). There are indications that Gauss had been in possession
of the geometric representation of complex numbers since 1796, but it went unpublished
until 1831, when he submitted his ideas to the Royal Society of Gottingen. Gauss introduced the term complex number
“If this subjet has hitherto been considered from the wrong viewpoint and thus
enveloped in mystery and surrounded by darkness, it is largely an unsuitable
terminology which should be blamed. Had +1, -1 and √−1, instead of being
called positive, negative and imaginary (or worse still, impossible) unity, been
given the names say,of direct, inverse and lateral unity, there would hardly have
been any scope for such obscurity.”
In a 1811 letter to Bessel, Gauss mentions the theorem that was to be known later as
Cauchy’s theorem. This went unpublished, and was later rediscovered by Cauchy and by
Weierstrass.
16. Augustin-Louis Cauchy (1789-1857) initiated complex function theory in an 1814 memoir
submitted to the French Acad´emie des Sciences. The term analytic function was not
mentioned in his memoir, but the concept is there. The memoir was published in 1825.
Contour integrals appear in the memoir, but this is not a first, apparently Poisson had
a 1820 paper with a path not on the real line. Cauchy constructed the set of complex
numbers in 1847 as R[x]/(x2 + 1)
“We completely repudiate the symbol √−1, abandoning it without regret because we do not know what this alleged symbolism signifies nor what meaning
to give to it.”