Im allgemeinen ist die relative Momentanbewegung zweier komplanarer ähnlich-veränderlicher Systeme als Spiralung um einen aufzufassen (Abb. J.). Die bei drei Systemen auftretenden drei Pole bestimmen einen
The paper deals with one-parametric projective plane motins with the property that all points of the inflexion cubic have straight trajectories. It is shown that such motions have in the general case projective equivalent trajectories and that the inflexion cubic is in general irreducible. The cases of the above mentioned motions with reducible inflexion cubic are discussed in detail. The connection with the Darboux property is also mentioned.
The paper is devoted to Euclidean space motions with two straight trajectories on two given skew straight lines. It describes all motions from this class which have one more planar trajectory in a plane not parallel to the given lines. In the conclusion it given conditions under which such motions have further planar trajectories in planes not parallel to the given skew straight lines.