In the course of his treatise On Burning Mirrors, he intended to facilitate the construction of surfaces to reflect light to a single point, he described the string construction of the ellipse and assumed a property of ellipses not found in Apollonius of Perga's Conics: the equality of the angles subtended at a focus by two tangents drawn from a point.
In his treatise "On Burning Mirrors," he sought to design surfaces that would reflect light to a single point, and he described the construction of an ellipse using string. He also proposed a unique property of ellipses not found in Apollonius of Perga's work: the equal angles subtended at a focus by two tangents drawn from a point.