The kappa curve, also known as Gutschoven's curve after Gérard van Gutschoven (1615–1668) who first studied it around 1662, resembles the Greek letter kappa (κ), It was also investigated by Isaac Newton and, some years later, by Johann Bernoulli. The kappa curve is given by the Cartesian equation:

 

   y ²(x ² + y ²) = a ²x ²