The principal object of the present Memoir is the establishment of the partial differential equation of the third order satisfied by the parameter of a family of surfaces belonging to a triple orthogonal system. It was first remarked by Bouquet that a given family of surfaces does not in general belong to an orthogonal system, but that (in order to its doing so) a condition must be satisfied: it was afterwards shown by Serret that the condition is that the parameter considered as a function of the coordinates must satisfy a partial differential equation of the third older, this equation was not obtained by him or the other French geometers engaged on the subject, although methods of obtaining it, essentially equivalent but differing in form, were given by Darboux and Levy.
A numerical algorithm for the third-order partial differential equation with time delay
