This paper deals with the curves which in German literature are called "Polortkurven". The application of these curves to problems in the field of synthesis of mechanisms has been described by P. Lohse in several of his papers . In this connection makes use of "Polortkuren" in the synthesis of four-bar linkages. In this connection he states a number of properties of these curves. Although his statements are for the greater part correct, the proofs are not given. It may therefore abe of interest provide these proofs.