Book Nahin, Paul J. (1998)
An imaginary tale: The story of [the square root of minus one]. (/isis/citation/CBB000076438/) unapi

Chapter Bölling, Reinhard (1997)
Kummer vor der Erfindung der “idealen complexen Zahlen”: Das Jahr 1844. In: Natur, Mathematik und Geschichte: Beiträge zur Alexander-von-Humboldt Forschung und zur Mathematikhistoriographie (p. 145). (/isis/citation/CBB000078499/) unapi

Article O'Neill, John (1986)
Formalism, Hamilton and complex numbers. Studies in History and Philosophy of Science (pp. 351-372). (/isis/citation/CBB000041051/) unapi

Chapter Neumann, Olaf (1981)
Über die Anstösse zu Kummers Schöpfung der “idealen complexen Zahlen”. In: Mathematical perspectives: Essays on mathematics and its historical development. Presented to Kurt-Reinhard Biermann on the occasion of his 60th birthday (p. 179). (/isis/citation/CBB000009648/) unapi

Article Pedersen, Kirsti Møller (1979)
Caspar Wessel and the representation of complex numbers. Nordisk Matematisk Tidsskrift (pp. 49-55). (/isis/citation/CBB000007450/) unapi

Article Dobrzycki, Stanislaw (1977)
O interpretacji geometrycznej logarytmów liczb zespolonych w rozprawie Karstena z 1768 g. (The geometric interpretation of the logarithmes of complex numbers in a work by W.J.G. Karsten in 1768.). Kwartalnik Historii Nauki i Techniki (pp. 529-534). (/isis/citation/CBB000019409/) unapi